3.10
イオン結合
より安定な電子配置になるため原子が電子を獲得したり失うと、原子はイオンを形成します。イオン結合は、反対の電荷を持つイオン間で生じる静電引力です。イオン性化合物は固体の時は硬くてもろく、水中ではそれらを構成するイオンに解離する場合があります。 対照的に、共有結合化合物は、化学反応によって破壊されない限…
An ionic bond is a non-covalent attraction that holds two oppositely charged ions together, such as the sodium cation and chloride anion in sodium chloride.
In this case, sodium transfers its single valence electron to chlorine. This electron transfer completes the octet of electrons in each combining atom, making them more stable.
The strength of an ionic bond depends on the environment of the ionic compound.
In the air, the ions remain closely packed in a solid crystal. Because there are no polar molecules to pull the ions apart, the strong attraction between opposite charges keeps the compound stable.
But in water, polar water molecules surround the ions and weaken their attraction. The partial negative charge on oxygen is attracted to sodium ions, while the partial positive charges on hydrogen are attracted to chloride ions. This pulls ions away from the crystal, causing the compound to break apart into its ions.
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Q1: What is an ionic bond and how does it form?
An ionic bond forms when one atom transfers electrons to another atom, creating oppositely charged ions that attract each other electrostatically. This electron transfer typically occurs between a metal and a nonmetal, where the metal loses electrons to become a positively charged cation and the nonmetal gains electrons to become a negatively charged anion. The strong electrostatic attraction between these opposite charges holds the compound together.
Q2: How do cations and anions differ in ionic compounds?
Cations are positively charged ions formed when an atom loses electrons, while anions are negatively charged ions formed when an atom gains electrons. In ionic compounds, cations and anions combine in specific ratios to achieve electrical neutrality. The number of electrons transferred determines the charge on each ion and the overall stability of the resulting ionic compound.
Q3: Why do ionic bonds typically form between metals and nonmetals?
Metals readily lose valence electrons because they have low ionization energy, while nonmetals readily gain electrons because they have high electron affinity. This difference in electron behavior makes electron transfer favorable between these element types. When a metal donates electrons to a nonmetal, both atoms achieve stable electron configurations, forming a strong ionic bond.
Q4: What role do valence electrons play in ionic bonding?
Valence electrons are the outermost electrons that participate in ionic bonding. Atoms transfer valence electrons to achieve a stable electron configuration, typically matching the nearest noble gas. The number of valence electrons an atom has determines how many electrons it will lose or gain, which directly affects the charge of the resulting ion and the formula of the ionic compound.
Q5: How do ionic compounds differ from covalent bonds in structure?
Ionic compounds consist of discrete cations and anions held together by electrostatic attraction, forming crystalline solids with repeating three-dimensional patterns. Covalent bonds, by contrast, involve shared electrons between atoms forming distinct molecules. Ionic compounds typically have higher melting points and conduct electricity when dissolved or melted, whereas covalent compounds are often molecular with lower melting points.
Q6: What determines the chemical formula of an ionic compound?
The chemical formula of an ionic compound is determined by the charges of the cation and anion. Ions combine in ratios that balance their charges to achieve electrical neutrality. For example, a cation with a +2 charge combines with two anions each with a -1 charge. This charge-balancing principle ensures the compound has no net electrical charge.
Q7: How does electrostatic attraction maintain ionic bond stability?
Electrostatic attraction is the force between oppositely charged ions that holds an ionic bond together. The strength of this attraction depends on the magnitude of the charges and the distance between ions. Stronger charges and closer proximity result in stronger ionic bonds. This electrostatic force is responsible for the high melting points and solid crystalline structure characteristic of ionic compounds.