Name: atomic mass and mole calculations
Uploaded: 2023-06-23T15:38:52.000Z
Duration: 1 min 25 s
Channel: JoVE

Masa atomowa pierwiastka, czasami nazywana masą atomową, jest w przybliżeniu równa sumie liczby protonów i neutronów. Jest to wyrażone w jednostkach masy atomowej, w skrócie amu lub daltony, i jest reprezentowane w pobliżu symbolu chemicznego w układzie okresowym pierwiastków.
Ale większość pierwiastków ma kilka izotopów, które różnią się liczbą neutronów, a tym samym ich masą.
W przypadku takich pierwiastków masa atomowa to średnia masa wszystkich izotopów pierwiastka, ważona zgodnie z ich względną obfitością lub procentem każdego izotopu występującego w przyrodzie.
Na przykład chlor ma dwa naturalnie występujące izotopy. Masa chloru-35 wynosi 34.97 amu, a chloru-37 36.97 amu.
Po pomnożeniu przez ich względną obfitość, 75,77% dla chloru-35 i 24,23% dla chloru-37, i zsumowaniu, otrzymujemy końcową masę atomową 35,45 amu.
Ponieważ chlor-35 występuje w przyrodzie w większej ilości niż chlor-37, masa atomowa chloru jest bliska 35 amu.

masa atomowa

Protony i neutrony mają mniej więcej taką samą masę, wynoszącą około 1,67 × 10^-24 gramów. Naukowcy arbitralnie definiują tę masę jako jednostkę masy atomowej (amu) lub jednego Daltona. Elektrony są o wiele lżejsze od protonów, ważąc jedynie 9,11 × 10^-28 gramów, co stanowi około 1/1800 jednostki masy atomowej. W rezultacie nie przyczyniają się one znacząco do ogólnej masy atomowej pierwiastka. Oznacza to, że przy rozważaniu masy atomowej, zazwyczaj zakłada się, że masa elektronów jest pomijalna, a masa atomu obliczana jest na podstawie liczby protonów i neutronów.

Jednakże, ponieważ większość naturalnie występujących pierwiastków składa się z izotopów, ważne jest uwzględnienie masy i naturalnej obfitości izotopów przy określaniu masy atomowej tych pierwiastków. Masa atomowa w takich przypadkach jest obliczana poprzez zsumowanie mas wszystkich izotopów pierwiastka, pomnożonych przez ich naturalną ułamkową obfitość.

Chemiści często używają jednostki "moli" do określania liczby atomów związku, które biorą udział w reakcji chemicznej. Molem pierwiastka jest jego masą atomową w gramach, podczas gdy moliem związku jest suma mas atomowych jego składników, nazywana masą cząsteczkową. Często używanym przykładem jest obliczanie mola glukozy o wzorze chemicznym C_6H_12O_6. Masa atomowa węgla (C) wynosi 12,011 gramów, a w glukozie jest sześć atomów węgla, co daje ogólną masę atomową 72,066 gramów. Wykonując te same obliczenia dla wodoru (H) i tlenu (O), masa cząsteczkowa glukozy wynosi 180,156 gramów.

Ten tekst jest adaptacją z <a href="https://openstax.org/books/biology-ap-courses/pages/2-1-atoms-isotopes-ions-and-molecules-the-building-blocks?query=atomic%20mass&target=%7B%22type%22%3A%22search%22%2C%22index%22%3A0%7D#fs-idp140338797859808">Openstax, Biology for AP</a><a href="https://openstax.org/books/biology-ap-courses/pages/2-1-atoms-isotopes-ions-and-molecules-the-building-blocks?query=atomic%20mass&target=%7B%22type%22%3A%22search%22%2C%22index%22%3A0%7D#fs-idp140338797859808">® </a><a href="https://openstax.org/books/biology-ap-courses/pages/2-1-atoms-isotopes-ions-and-molecules-the-building-blocks?query=atomic%20mass&target=%7B%22type%22%3A%22search%22%2C%22index%22%3A0%7D#fs-idp140338797859808">courses. Section 2.1 Atoms, Isotopes, Ions, and Molecules: The Building Blocks</a> and <a href="https://openstax.org/books/anatomy-and-physiology-2e/pages/2-4-inorganic-compounds-essential-to-human-functioning?query=mole&target=%7B%22type%22%3A%22search%22%2C%22index%22%3A0%7D#fs-id1218107">Openstax, Anatomy and Physiology 2e, Section 2.4 Inorganic compounds Essential to Human Functioning</a>

Masa atomowa

Protony i neutrony mają w przybliżeniu taką samą masę, około 1,67 × 10-24 gramów. Naukowcy arbitralnie definiują tę ilość masy jako jedną masę atomową ...

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Atomic Weight

atomic mass and mole calculations

Atomic mass and mole calculations help explain how much matter is in atoms and compounds. Protons and neutrons have about the same mass, about 1.67 × 10 -24 grams. Scientists define that mass as one atomic mass unit, or amu, also called one Dalton.

Electrons are much lighter than protons. They weigh only 9.11 × 10 -28 grams, or about 1/1800 of an atomic mass unit. Because of that small mass, electrons do not add much to an element’s overall atomic mass. When chemists calculate atomic mass, they usually ignore electrons and use only the protons and neutrons.

Many naturally occurring elements are made of isotopes, which are atoms of the same element with different masses. For these elements, atomic mass must include each isotope’s mass and its natural fractional abundance. Chemists find this by adding the masses of all the isotopes after multiplying each one by how common it is.

Chemists also use the mole to count atoms and compounds in reactions. A mole of an element is its atomic weight in grams. A mole of a compound is the sum of the atomic weights of its parts, and that total is called the molecular weight. Glucose, C6H12O6, is a common example. Carbon has an atomic weight of 12.011 grams, and six carbons in glucose give 72.066 grams. Doing the same for hydrogen and oxygen gives glucose a molecular weight of 180.156 grams.

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Atomic Mass and Mole Calculations

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