Atoms: the Building Block of Matter

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CHEMISTRY CHAPTER 3

(Atoms: The Building Block of Matter)

The Law of Conservation of Mass

Mass is neither destroyed nor created during ordinary chemical reactions or physical changes.

The Law of Definite Proportions

A chemical compound contains the same elements in exactly the same proportions by mass

An atom is the smallest particle of an element that retains the properties of that element

All matter is made up of atoms

The nucleus is the very small dense positively charged central part of an atom

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An atoms electron cloud is the region in which the electrons orbit the nucleus

An electron cloud is made up of negatively charged particles called electrons

Electrons orbiting a nucleus at a certain distance is said to be on the same energy level

An energy level is a particular area in which one or more electrons orbit the nucleus

Only a certain number of electrons can occupy the same energy level

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Protons are positively charged particles [in the nucleus of an atom]

Neutrons are neutral particles [in the nucleus of an atom]

The atomic number is the number of protons in the nucleus of an atom

Li Atomic number = 3

so,

3 protons

3 neutrons

3 electrons

The mass number is the total number of protons and neutrons in the nucleus of an isotope.

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Atoms of the same element that have different masses (different number of neutrons) are called isotopes

Ex: The three isotopes of Hydrogen

Hydrogen-1 Hydrogen-2 Hydrogen-3

(protium) (duetrium) (tritium)

mass # = 1 mass # = 2 mass # = 3

A nuclide is a general term for any isotope of any element

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The number 6.02 x 1023 is referred to as a mole

6.02 x 1023 is the Avogadro number

6.02 x 1023 = 602,000,000,000,000,000,000,000

six hundred, two hextillion

The Average-atomic weight(Atomic mass) of an element is equal to the mass of one mole of atoms

This number can be found on the periodic chart.

*Each of the following are used as synonyms for average-atomic mass:

gram formula weight(GFW)

gram molecular weight(GMW) (most common use)

molecular weight(MW)

formula weight(FW)

formula mass(FM)

and others