Unit 2: Atomic Stucture

Atomic Structure

Atom: the smallest particle of an element that retains the chemical properties of that element

Population of the world in 2000: 6 000 000 000
Atoms in a penny:29 000 000 000 000 000 000 000 (2.9 x 10^22)

Diameter of a copper atom: 1.28 x 10^-10 m
(6 billion copper atoms side by side would give a line of copper less than one meter long)

Subatomic Particles

Protons (p+) positively charged particles with a mass of 1.673 x 10^-24 g and a charge of +1; located in the nucleus of an atom.

Neutrons (n°) electrically neutral particles with a mass of 1.675 x 10^-24 g located in the nucleus of an atom.

Electrons (e-): negatively charged particles with a mass of 9.11 x 10^-28 g and a charge of -1; located in the space around the nucleus.

**THE MAJORITY OF AN ATOM'S MASS IS LOCATED IN THE NUCLEUS**

Atomic Number and Mass Number
Atomic Number (Z) – the number of protons in the nucleus of an atom of any particular element

Since atoms are neutral in charge, the number of electrons must equal the number of protons.

Mass Number (A) – the number of protons and neutrons in the atom’s nucleus (rounded whole number of the atomic mass)

Because all atoms of a given element have the same atomic number, the subscript is redundant and often omitted, therefore, it is written as 39K