The Atom

Unit III

Picture it….

Draw a picture of a Helium particle and a Xenon particle.

Similarities: Both are atoms.Difference? Mass

He: 4.0 g/moleXe: 131 g/mole

Why???

Xenon has more stuff in it. So, what’s in an atom?Protons = positive charge =p+

Electrons = negative charge = e-

Neutrons = neutral charge = n0

Now, draw a picture of the Helium atom, show how the subatomic particles are arranged.

The Helium Atom

= proton

= neutron

= electron

Atomic Number (Z):Identifies the element.Number of protons. Whole number (Blue) on periodic table.For a neutral atom the # of protons is equal to the number of electrons.

ISOTOPES: Atoms that have the same number of protons but different number of neutrons.Mass Number (A):

Unique for each isotope. Number of p+ + number of no

Not found on periodic table.C-12 vs. C-14

Identify the # of subatomic particlesElement #

protons# electrons

Mass # Atomic # #neutrons

Li 7

Ca 20

46 62

15 31

Atomic Mass:Also called atomic weight or molar mass.Weighted average mass for one mole of all isotopes.Decimal number found on P.T.

Atomic Mass = (mass1)(relative abundance1) + (mass2)(relative abundance2) +………..

Example: Calculate the atomic mass of chlorine. The two isotopes have atomic masses and relative abundance of 34.97 amu (75.77%) and 36.97 amu (24.23%).