Name: measurement: si units and conversions
Uploaded: 2020-09-03T13:38:25.000Z
Duration: 3 min 38 s
Channel: JoVE

K12 Standards

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

9-12

Chemistry

Structure And Properties Of Matter

Quantifying matter

Measurement: Standard Units

在科学中，测量是赋予给 一个数值一种特性，如物质的质量、大小和温度。每种测量都会提供两种信息。第一个是数字 测量的大小 或量级。第二个是单位 这是测量的 比较标准。所以，当水在 100°C 下沸腾时，数字 100 代表测量值，C 摄氏度）代表单位。放在一起，它们传达了有关物质 性质的相对大小 沸点。如果没有单位，一个数字可能毫无意义或令人困惑。例如，如果埃菲尔铁塔的高度 报告为 300，而没有提供单位 这个数字 300 的上下文并不清楚。这意味着埃菲尔铁塔可能相对较高，也可能很矮…但如果没有可比较的单位，这就很难去评估。有时候，还会提供第三种形式的信息，即误差。这些数据表明了测量的 不确定度。因此，为了准确地测量和报告 物质的各种性质，人们开发了通用的测量系统。国际单位制，也称为SI单位制 是科学家普遍使用的单位制。在国际单位制下，7 种基本特性 的测量单位 长度、质量、时间、温度、电流、物质的量、和发光强度，都被固定下来。这些被称为标准单位，或基本单位。其中，前四种性质的基本单位 是化学中最常用的。国际单位制中长度的标准单位 是米，用单位符号"m"表示。较长的距离通常在报告中 用公里或"km"表示，其中 1 公里 等于 1000 米。相反地，较短的距离可以 用厘米或"cm"表示，其中 1 厘米 等于 0.01 米；或毫米，mm"其中 1 毫米等于 0.001 米。同样地，国际单位制中质量的标准单位 是千克，用单位符号"kg"表示。一千克等于 1000 克。温度是另一个基本属性，国际单位制为开尔文，单位符号为大写的"K"这里显示时没有带"degree"一词或degree 的符号，以区别于摄氏度和 华氏度。例如，水在 373.15 K 下沸腾，人体的正常体温 约为 310 K。第四种最常用的基本单位 是秒，即时间的国际单位制，单位符号为"s"较短的时间间隔可以用毫秒表示，其中 1 毫秒等于 0.001 秒，而较长的时间间隔可以 用兆秒表示，其中1兆秒 等于100万秒。或者，非国际单位制，如小时、天和年。也可以被使用。

测量：标准单位

每项测量都提供三种类型的信息：测量的大小或幅度 (数字) ，测量的比较标准 (单位) 以及测量不确定性的指示。 当写入数量时，数字和单位会被明确表示，但不确定性是测量结果中错误的一个方面。 
 
 测量中的数值可以用不同的方式表示，包括十进制形式和科学记数法，后者也称为指数记数法。 例如，波音 777-200ER 客机的最大起飞重量为 298,000 公斤，也可以写入 2.98 × 105 公斤。  
 
 单位 (如升，磅和厘米) 是测量的比较标准。 一瓶 2 升软饮料包含的饮料量是 1 升可接受体积的两倍。 如果没有单位，数字可能毫无意义，混乱或可能危及生命。 假设医生开具苯巴比妥药来控制患者的癫痫发作，并在没有具体说明单位的情况下说明剂量为“ 100 ”。 这不仅会使给予剂量的医务人员感到困惑，而且后果可能是可怕的： 100 毫克每天三次可以作为抗痉挛药有效，但 100 克的单剂量是致命剂量的 10 倍以上。 
 
 <h4>国际单位制 (SI 单位) </h4>
 
 七个基本性质 (“基本单位”) 的测量单位：长度、质量、时间、温度、电流、物质含量和发光强度已由国际协定确定。 它们被称为国际单位体系或 SI 单位。 其他性质的单位可能来自这七个基本单位。 日常测量单位通常被定义为其他单位的分数或倍数。 牛奶通常包装在 1 加仑 (4 夸脱) ， 1 夸脱 (0.25 加仑) 和一品脱 (0.5 夸脱) 的容器中。 这种方法也用于 SI 单位，但这些分数或倍数始终是 10 的幂。 使用前缀和基本单位的名称来命名分次或多个 SI 单位。 例如， 1000 米的长度也称为公里，因为前缀 kilo 表示“一千”，科学记数为 103 (1 公里 = 1000 米 = 103 米)。 
 
 <h4>标准国际单位制（SI 单位）</h4>
 
 法国在法国革命期间建立了最终演变为国际单位制的度量系统的最初单位。 最初的米和千克标准在1799年在那里采用，最终被其他国家采纳。 以下是化学中常用的四个 SI 基体单位。 
 
 <h4>1 长度 </h4>
 
 SI 系统中的标准长度单位是米 (m)。 一个仪表的定义是距离指示灯在真空中以1/299,792,458秒的间隔运动。 较长的距离通常以公里为单位 (1 km = 1000 m = 103 m) ，而较短的距离可以以厘米 (1 cm = 0.01 m = 10−2 m) 或毫米 (1 mm = 0.001 m = 10−3 m) 为单位报告。 
 
 <h4>2. 质量 </h4>
 
 SI 系统中的标准质量单位是公斤 (kg千克)。 一公斤由基准物体的质量定义 - 一种由铂铱合金制成的金属气缸，高度和直径为 39 毫米。 任何质量与本参考相同的物体均被认为质量为 1 公斤。 克 (g) 完全等于公斤 / 千克 (10−3 千克) 的千分之一（ 1/1000）。 
 
 “重量”一词通常与“质量”交替使用。 但是，这两种数量不同。 物体的质量衡量物体内物质的数量，而物体的重量则衡量对其物质施加的引力。 例如，如果我们能够在重力比地球弱的月球上称重，我们的体重就会比在地球上减轻。 但是，质量——我们身体中物质的数量——将保持不变。 
 
 <h4>3. 温度 </h4>
 
 温度的SI单位是开尔文（K），尽管在SI系统中也允许使用摄氏度（°C），同时使用“度”和度的符号进行摄氏度测量。 摄氏度度与开尔文（开氏度 / 华氏度）的幅度相同，但这两个刻度将其零放置在不同的位置。 根据定义，水在 273.15 K (0 °C) 时冻结，在 373.15 K (100 °C) 时沸腾，人体正常体温约为 310 K (37 °C)。 华氏度 (°F) 刻度是另一种用于测量温度的常用单位。 以华氏度计，水在 32 °F 时冻结，在 212 °F 时沸腾，人体正常温度为 96 °F  
 
 尽管华氏度和摄氏度刻度允许负温度，但开尔文刻度 (也称为绝对刻度) 却不允许负温度。在开尔文刻度上， 0 K 为最低温度，即绝对零。  
 
 使用以下转换公式可互换温度标度： 
 
 <img alt="Eq1" src="https://www.jove.com/files/core/CDNSource/lessons/1010/1010_Equations-01.png" style="height: 40px;" />
 
 <img alt="Eq2" src="https://www.jove.com/files/core/CDNSource/lessons/1010/1010_Equations-02.png" style="height: 40px;" />
 
 <h4>4. 时间 </h4>
 
 SI的基本时间单位是秒 (s)。 可以使用适当的前缀来表示较小和较大的时间间隔。 例如：  
 
 <img alt="Eq3" src="https://www.jove.com/files/core/CDNSource/lessons/1010/1010_Equations-03.png" style="height: 40px;" />
 
 <img alt="Eq4" src="https://www.jove.com/files/core/CDNSource/lessons/1010/1010_Equations-04.png" style="height: 40px;" />
 
 或者，可以使用小时、天和年。 
 
 本文改编自 <a href="https://openstax.org/books/chemistry-2e/pages/1-4-measurements">Openstax, 化学 2e, 第 1.4 节：测量。</a>

每次测量都提供三种信息：测量的大小或数值（一个数字）、测量的比较标准……

Education

教育

JoVE Core

化学

Introduction: Matter and Measurement

导论：物质与测量

KEY TERMS AND CONCEPTS

关键术语与概念

measurement: si units and conversions

Measurement gives three kinds of information: a number, a unit, and an estimate of uncertainty. The number shows size or magnitude. The unit gives a standard for comparison. The uncertainty reflects possible error in the measurement.

Numbers can be written in more than one way. A value may appear in decimal form or in scientific notation, which is also called exponential notation. For example, the maximum take-off weight of a Boeing 777-200ER airliner is 298,000 kilograms, or 2.98 × 10^5 kg.

Units are essential because they make a number meaningful. Common units such as liters, pounds, and centimeters help people compare measurements. A 2-liter bottle of soft drink contains twice the volume of a 1-liter bottle. Without units, a number can be confusing or even dangerous. A doctor who writes a dose as “100” without units could create a serious mistake, because 100 mg taken three times a day can be effective, while 100 g is more than 10 times the lethal amount.

The International System of Units, or SI units, is based on seven fundamental properties called base units. These properties are length, mass, time, temperature, electric current, amount of substance, and luminous intensity. Other units are derived from these base units. Everyday units often use fractions or multiples of a base unit, and SI units do the same with powers of 10. Prefixes show these multiples. For example, kilo means one thousand, so 1 kilometer equals 1000 meters, or 10^3 m.

The metric system began in France during the French Revolution. The original standards for the meter and kilogram were adopted in 1799 and later used by other countries. In chemistry, the four SI base units used most often are length, mass, temperature, and time.

The SI unit of length is the meter, or m. A meter is defined as the distance light travels in a vacuum in 1/299,792,458 of a second. Longer distances are often given in kilometers, while shorter distances are often given in centimeters or millimeters. These units relate directly to the meter: 1 km = 1000 m = 10^3 m, 1 cm = 0.01 m = 10^-2 m, and 1 mm = 0.001 m = 10^-3 m.

The SI unit of mass is the kilogram, or kg. It is defined by a reference object, a metal cylinder made from platinum-iridium alloy with a height and diameter of 39 mm. Any object with the same mass as that reference has a mass of 1 kilogram. The gram, or g, is exactly 1/1000 of a kilogram, which is 10^-3 kg. Weight is often used like mass, but they are not the same. Mass is the amount of matter in an object, while weight is the gravitational force on that matter. That is why a person would weigh less on the moon, where gravity is weaker, but the mass would stay the same.

The SI unit of temperature is the kelvin, or K, although degree Celsius, or °C, is also allowed in SI. Celsius and kelvin have the same size unit, but their zero points are different. Water freezes at 273.15 K, which is 0 °C, and boils at 373.15 K, which is 100 °C. Normal human body temperature is about 310 K, or 37 °C. Fahrenheit, or °F, is another common scale. On that scale, water freezes at 32 °F and boils at 212 °F, and normal body temperature is 96 °F. Celsius and Fahrenheit can show negative temperatures, but Kelvin cannot. The Kelvin scale starts at 0 K, called absolute zero. Temperature scales can be converted using the given formulas.

The SI base unit of time is the second, or s. Small and large time intervals can be written with prefixes, and hours, days, and years are also used. Together, these units help scientists and students describe measurements clearly and compare results with confidence.

Measurement: SI Units and Conversions

scientific laws and theories

How Science Explains Laws and Theories

Scientific laws and scientific theories describe science in two different ways. A law is a concise verbal or mathematical statement that summarizes many experimental observations. It describes or predicts aspects of the natural world that stay the same under the same conditions. A scientific theory is different because it explains why natural events happen. It is a unifying principle that gives a well-supported and testable explanation for a broad set of observations. Strong theories are the...

the scientific method

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physical and chemical properties of matter

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Distinguishing Physical and Chemical Changes

Matter can be identified by its properties, which are the features that help us tell one substance from another. These properties fall into two main groups: physical properties and chemical properties. Understanding the difference helps explain how matter changes. A physical property is a feature of matter that is not linked to a change in chemical composition. Examples include density, color, hardness, melting point, boiling point, and electrical conductivity. Some physical properties can be...

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States of matter help describe how matter behaves in chemistry. Matter is anything that has mass and takes up space. It is found everywhere, including air, water, soil, mountains, and even our bodies. The three common states on Earth are solid, liquid, and gas. A solid has a definite shape and a definite volume. Its particles, such as atoms or molecules, are packed very closely together and held in place by strong forces, so they only vibrate slightly. This tight arrangement makes solids...

measurement: standard units

Measurement gives three kinds of information: a number, a unit, and an estimate of uncertainty. The number shows size or magnitude. The unit gives a standard for comparison. The uncertainty reflects possible error in the measurement. Numbers can be written in more than one way. A value may appear in decimal form or in scientific notation, which is also called exponential notation. For example, the maximum take-off weight of a Boeing 777-200ER airliner is 298,000 kilograms, or 2.98 × 10^5 kg. <br...

classifying matter by composition

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measurement: derived units

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uncertainty in measurement: accuracy and precision

uncertainty-in-measurement-accuracy-and-precision

Measurement Error: Reading Results Correctly

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uncertainty in measurement: reading instruments

uncertainty-in-measurement-reading-instruments

Measurement Uncertainty and Significant Figures

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uncertainty in measurement: significant figures

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Measurement: SI Units and Conversions | JoVE K12

chemistry

JoVE Core 化学通过简单明了且通俗易懂的动画视频课程，将普通化学概念带入到现实生活当中。此外，在科学家行动视频中，我们演示了在实验室中进行的经典和原始研究实验。

Texas Essential Knowledge and Skills

High School

Specialised Topic in Science

112.51.c.1.

112.51.c.1.E.

CHEM.1

CHEM.1.E

Biology

BIO.1

BIO.1.E

The Atomic Theory of Matter

The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers. Leucippus and Democritus argued that all matter ...

The Bohr Model

Following the work of Ernest Rutherford and his colleagues in the early twentieth century, the picture of atoms consisting of tiny dense nuclei surrounded ...

The Quantum-Mechanical Model of an Atom

Shortly after de Broglie published his ideas that the electron in a hydrogen atom could be better thought of as being a circular standing wave instead of ...

Subatomic Particles

Dalton was only partially correct about the particles that make up matter. All matter is composed of atoms, and atoms are composed of three smaller ...

Quantum Numbers

It is said that the energy of an electron in an atom is quantized; that is, it can be equal only to certain specific values and can jump from one energy ...

Atomic Orbitals

An atomic orbital represents the three-dimensional regions in an atom where an electron has the highest probability to reside. The radial distribution ...

The Pauli Exclusion Principle

The arrangement of electrons in the orbitals of an atom is called its electron configuration. We describe an electron configuration with a symbol that ...

The Energies of Atomic Orbitals

In an atom, the negatively charged electrons are attracted to the positively charged nucleus. In a multielectron atom, electron-electron repulsions are ...

The Aufbau Principle and Hund's Rule

To determine the electron configuration for any particular atom, we can build the structures in the order of atomic numbers. Beginning with hydrogen, and ...

electron-configuration-of-multielectron-atoms

Electron Configuration of Multielectron Atoms

The alkali metal sodium (atomic number 11) has one more electron than the neon atom. This electron must go into the lowest-energy subshell available, the ...

Thomson's e/m Experiment

In a beam of charged particles created by a heated cathode, the particles move at different speeds. However, many applications need a beam with uniform ...

Atomic structure
• Evolution of atomic models/theory
• Electrons
• Electron configurations

Content elaboration: Physical Science included properties and locations of protons, neutrons and electrons, atomic number, mass number, cations and anions, isotopes and the strong nuclear force which holds the nucleus together. In this course, the historical development of the atomic model and the positions of electrons are explored in greater detail. Atomic models are constructed to explain experimental evidence and make predictions. The changes in the atomic model over time exemplify how scientific knowledge changes as new evidence emerges and how technological advancements like electricity extend the boundaries of scientific knowledge. Thompson's study of electrical discharges in cathode-ray tubes led to the discovery of the electron and the development of the plum pudding model of the atom. Rutherford's experiment, in which he bombarded gold foil with a-particles, led to the discovery that most of the atom consists of empty space with a relatively small, positively charged nucleus. Bohr used data from atomic spectra to propose a planetary model of the atom in which electrons orbit the nucleus, like planets around the sun. Later, Schrödinger used the idea that electrons travel in waves to develop a model in which electrons travel randomly in regions of space called orbitals (quantum mechanical model). Based on the quantum mechanical model, it is not possible to predict exactly where electrons are located but there is a region of space surrounding the nucleus in which there is a high probability of finding an electron (electron cloud or orbital). Data from atomic spectra (emission and absorption) gives evidence that electrons can only exist at certain discrete energy levels and not at energies between these levels. Atoms are usually in the ground state where the electrons occupy orbitals with the lowest available energy. However, the atom can become excited when the electrons absorb a photon with the precise amount of energy (indicated by the frequency of the photon) to move to an orbital with higher energy. Any photon without this precise amount of energy will be ignored by the electron. The atom exists in the excited state for a very short amount of time. When an electron drops back down to the lower energy level, it emits a photon that has energy equal to the energy difference between the levels. The amount of energy is indicated by the frequency of the light that is given off and can be measured. Each element has a unique emission and absorption spectrum due to its unique electron configuration and specific electron energy jumps that are possible for that element. Being aware of the quantum mechanical model as the currently accepted model for the atom is important for science literacy as it explains and predicts subatomic interactions, but details should be reserved for more advanced study. Electron energy levels consist of sublevels (s, p, d and f), each with a characteristic number and shape of orbitals. Orbital diagrams and electron configuration can be constructed to show the location of the electrons in an atom using established rules. Valence electrons are responsible for most of the chemical properties of elements. In this course, electron configuration (extended and noble gas notation) and orbital diagrams can be shown for any element in the first three periods. Although the quantum mechanical model of the atom explains the most experimental evidence, other models can still be helpful. Thinking of atoms as indivisible spheres is useful in explaining many physical properties of substances, such as the state (solid, liquid or gas) of a substance at room temperature. Bohr's planetary model is useful to explain and predict periodic trends in the properties of elements.

Atomic structure

The Periodic Table

As early chemists discovered more elements, they realized that various elements could be grouped by their similar chemical behaviors. One such grouping ...

Periodic Classification of the Elements

The periodic table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. When their ...

atomic-radii-and-effective-nuclear-charge

Atomic Radii and Effective Nuclear Charge

The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number ...

Ionic Radii

Ionic radius is the measure used to describe the size of an ion. A cation always has fewer electrons and the same number of protons as the parent atom; it ...

Ionization Energy

The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy ...

Electron Affinity

The electron affinity (EA) is the energy change for adding an electron to a gaseous atom to form an anion (negative ion).



This process can be either ...

Alkali Metals

Group 1 elements are soft and shiny metallic solids. They are malleable, ductile, and good conductors of heat and electricity. The melting points of the ...

Halogens

Group 17 elements, known as halogens, are nonmetals. At room temperature, fluorine and chlorine are gases, bromine is a liquid, and iodine a solid. ...

Noble Gases


The elements in group 18 are noble gases (helium, neon, argon, krypton, xenon, and radon). They earned the name &ldquo;noble&rdquo; because they were ...

Periodic Table
• Properties
• Trends

Content elaboration: In the Physical Science course, the concept that elements are placed in order of increasing atomic number in the periodic table such that elements with similar properties are placed in the same column is introduced. How the periodic table is divided into groups, families, periods, metals, nonmetals and metalloids is also included and will be revisited here. In this course, with more information about the electron configuration of elements, similarities in the configuration of the valence electrons for a particular group can be observed. The electron configuration of an atom can be determined from the position on the periodic table. The repeating pattern in the electron configuration for elements on the periodic table explains many of the trends in the properties observed. Atomic theory is used to describe and explain trends in properties across periods or down columns including atomic radii, ionic radii, first ionization energies, electronegativities and whether the element is a solid or gas at room temperature. Additional ionization energies, electron affinities and periodic properties of the transition elements, and the lanthanide and actinide series are reserved for more advanced study.

Periodic Table

Types of Chemical Bonds

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Lewis Symbols and the Octet Rule

Chemical bonds are complex interactions between two or more atoms or ions, which reduce the potential energy of the molecule. Gilbert N. Lewis developed a ...

Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

The Born-Haber Cycle

Lattice Energy&#xA0;

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a ...

trends-in-lattice-energy-ion-size-and-charge

Trends in Lattice Energy: Ion Size and Charge

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a compound is a measure ...

Covalent Bonding and Lewis Structures

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Electronegativity

Whether a bond is nonpolar or polar covalent is determined by a property of the bonding atoms called electronegativity.&#xA0;

Electronegativity values of ...

bond-polarity-dipole-moment-and-percent-ionic-character

Bond Polarity, Dipole Moment, and Percent Ionic Character

Bond Polarity

The absolute value of the difference in electronegativity (&Delta;EN) of two bonded atoms provides a rough measure of the polarity to be ...

lewis-structures-of-molecular-compounds-and-polyatomic-ions

Lewis Structures of Molecular Compounds and Polyatomic Ions

To draw Lewis structures for complicated molecules and molecular ions, it is helpful to follow a step-by-step procedure as outlined:


	Determine the ...

Resonance

The Lewis structure of a nitrite anion (NO2&minus;) may actually be drawn in two different ways, distinguished by the locations of the N-O and N=O ...

Formal Charges

In some cases, there are seemingly more than one valid Lewis structures for molecules and polyatomic ions. The concept of formal charges can be used to ...

Exceptions to the Octet Rule

Many covalent molecules have central atoms that do not have eight electrons in their Lewis structures. These molecules fall into three categories:


	...

Bond Energies and Bond Lengths

Stable molecules exist because covalent bonds hold the atoms together. The strength of a covalent bond is measured by the energy required to break it, ...

VSEPR Theory and the Basic Shapes

Overview of VSEPR Theory

Valence shell electron-pair repulsion theory (VSEPR theory) enables us to predict the molecular structure, including approximate ...

vsepr-theory-and-the-effect-of-lone-pairs

VSEPR Theory and the Effect of Lone Pairs

Effect of Lone Pairs of Electrons&nbsp;on Molecule Geometry

It is important to note that electron-pair geometry around a central atom is not the same ...

Predicting Molecular Geometry

VSEPR Theory for Determination of Electron Pair Geometries

The following procedure uses VSEPR theory to determine the electron pair geometries and the ...

Molecular Shape and Polarity

Dipole Moment of a Molecule

Polar covalent bonds connect two atoms with differing electronegativities, leaving one atom with a partial positive charge ...

Valence Bond Theory

Overview of Valence Bond Theory

Valence bond theory describes a covalent bond as the overlap of half-filled atomic orbitals (each containing a single ...

Hybridization of Atomic Orbitals I

The mathematical expression known as the wave function, &#x3C8;, contains information about each orbital and the wavelike properties of electrons in an ...

Hybridization of Atomic Orbitals II

sp3d and sp3d&nbsp;2 Hybridization

To describe the five bonding orbitals in a trigonal bipyramidal arrangement, we must use five of the valence shell ...

Molecular Orbital Theory I

Overview of Molecular Orbital Theory

Molecular orbital theory describes the distribution of electrons in molecules in the same way as the distribution of ...

Molecular Orbital Theory II

Molecular Orbital Energy Diagrams

The relative energy levels of atomic and molecular orbitals are typically shown in a molecular orbital diagram. For a ...

Bonding in Metals

Metallic bonds are formed between two metal atoms. A simplified model to describe metallic bonding has been developed by Paul Dr&#xFC;de called the ...

Chemical bonding
• lonic
• Polar/covalent

Content elaboration: Content in the Physical Science course included recognizing that atoms with unpaired electrons tend to form ionic and covalent bonds with other atoms, forming molecules, ionic lattices or network covalent structures. In this course, electron configuration, electronegativity values and energy considerations will be applied to bonding and the properties of materials with different types of bonding. Atoms of many elements are more stable when they are bonded to other atoms. In such cases, as atoms bond, energy is released to the surroundings, resulting in a system with lower energy. An atom's electron configuration, particularly the valence electrons, determines how an atom interacts with other atoms. Molecules, ionic lattices and network covalent structures have different, yet predictable, properties that depend on the identity of the elements and the types of bonds formed. Differences in electronegativity values can be used to predict where a bond fits on the continuum between ionic and covalent bonds. The polarity of a bond depends on the electronegativity difference and the distance between the atoms (bond length). Polar covalent bonds are introduced as an intermediary between ionic and pure covalent bonds. The concept of metallic bonding is also introduced to explain many of the properties of metals (e.g., conductivity). Since most compounds contain multiple bonds, a substance may contain more than one type of bond. Carbon atoms can bond together and with other atoms, especially hydrogen, oxygen, nitrogen and sulfur, to form chains, rings and branching networks that are present in a variety of important compounds, including synthetic polymers, fossil fuels and the large molecules essential to life.

Chemical bonding

Chemical Formulas

A chemical formula presents information about the proportions of atoms constituting a particular chemical compound or molecule, mainly using symbols of ...

ionic-compounds-formulas-and-nomenclature

Ionic Compounds: Formulas and Nomenclature

An element composed of atoms that readily lose electrons (a metal) can react with an element composed of atoms that readily gain electrons (a nonmetal) to ...

molecular-compounds-formulas-and-nomenclature

Molecular Compounds: Formulas and Nomenclature

Molecular compounds or covalent compounds result when atoms share electrons to form covalent bonds. Since there is no electron transfer, molecular ...

Organic Compounds

All living things are formed mostly of carbon compounds called organic compounds. The category of organic compounds includes both natural and synthetic ...

Classification of Elements and Compounds

Pure substances consist of only one type of matter. A pure substance can be an element or a compound. An element consists of only one type of atom, while ...

Molecular Models

Physical models representing molecular architectures of chemical compounds play essential roles in understanding chemistry. The use of molecular models ...

Representing compounds
• Formula writing
• Nomenclature
• Models and shapes (Lewis structures, ball and stick, molecular geometries)

Content elaboration: Using the periodic table, formulas of ionic compounds containing specific elements can be predicted. This can include ionic compounds made up of elements from groups 1, 2, 17, hydrogen, oxygen and polyatomic ions (given the formula and charge of the polyatomic ion). Given the formula, a compound can be named using conventional systems that include Greek prefixes and Roman numerals where appropriate. Given the name of an ionic or covalent substance, formulas can be written. Many different models can be used to represent compounds including chemical formulas, Lewis structures, and ball and stick models. These models can be used to visualize atoms and molecules and to predict the properties of substances. Each type of representation provides unique information about the compound. Different representations are better suited for particular substances. Lewis structures can be drawn to represent covalent compounds using a simple set of rules and can be combined with valence shell electron pair repulsion (VSEPR) theory to predict the three-dimensional electron pair and molecular geometry of compounds. Lewis structures and molecular geometries will only be constructed for the following combination of elements: hydrogen, carbon, nitrogen, oxygen, phosphorus, sulfur and the halogens.

Representing compounds

Every measurement provides three kinds of information: the size or magnitude of the measurement (a number), a standard of comparison for the measurement ...

Measurement: Derived Units

The International System of Units or SI system, by international agreement, has fixed measurement units for seven fundamental properties: length, mass, ...

Uncertainty in Measurement: Accuracy and Precision

Scientists typically make repeated measurements of a quantity to ensure the quality of their findings and to evaluate both the precision and the accuracy ...

Uncertainty in Measurement: Reading Instruments

Counting is the type of measurement that is free from uncertainty, provided the number of objects being counted does not change during the process. Such ...

Uncertainty in Measurement: Significant Figures

All the digits in a measurement, including the uncertain last digit, are called significant figures or significant digits. Note that zero may be a ...

Dimensional Analysis

Dimensional analysis, also known as the factor label method, is a versatile approach for mathematical operations. The main principle behind this approach ...

Quantifying matter

Content elaboration: In earlier grades, properties of materials were quantified with measurements that were always associated with some error. In this course, scientific protocols for quantifying the properties of matter accurately and precisely are studied. Using the International System of Units (SI), significant digits or figures, scientific notation, error analysis and dimensional analysis are vital to scientific communication. There are three domains of magnitude in size and time: the macroscopic (human) domain, the cosmic domain and the submicroscopic (atomic and subatomic) domain. Measurements in the cosmic domain and submicroscopic domains require complex instruments and/or procedures. Matter can be quantified in a way that macroscopic properties such as mass can reflect the number of particles present. Elemental samples are a mixture of several isotopes with different masses. The atomic mass of an element is calculated given the mass and relative abundance of each isotope of the element as it exists in nature. Because the mass of an atom is very small, the mole is used to translate between the atomic and macroscopic levels. A mole is equal to the number of atoms in exactly 12 grams of the isotope carbon-12. The mass of one mole of a substance is equal to its molar mass in grams. The molar mass for a substance can be used in conjunction with Avogadro's number and the density of a substance to convert between mass, moles, volume and number of particles of a sample.

Measurement: SI Units and Conversions

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