Chemistry

The structure of the atom.

The Atomic Theory:

• All matter is made of atoms, which are particles too small to be seen.

• Each element has its own kind of atom.

The evolution of the atomic Theory:

1. Dalton

2. Rutherford’s gold foil experiment

3. Bohr models

4. Quantum MechanicsAll matter is composed of atoms

Atoms cannot be made or destroyedAll atoms of the same element are identical

Different elements have different types of atomsChemical reactions occur when atoms are

rearrangedCompounds are formed from atoms of the

different elements coming together.

Sub Atomic Particles

Subatomic Particle

Charge Mass (Amu)

Atomic mass units

Where it is located in an atom

Proton

Neutron

Electron

+

Basically 0

10

-

Inside the nucleus1

Orbiting outside the nucleus

Inside the nucleus

The Modern Theory of Atomic Structure:

• Atomic number: The number of protons in the nucleus of an atom of that element.– Gives the number of electrons in a neutral

element.– Gives the order of elements on the periodic

table– If an atom gains or loses a proton it not only

changes its atomic number, it also becomes a new element.

The Modern Theory of Atomic Structure:

• Mass number: is the total number of protons and neutrons in the nucleus of an atom

• How do we find the number of Neutrons?

(mass number) - (atomic number) =# of neutrons

Bohr’s Model of Electrons:

• Suggested that electrons move around the nucleus of an atom in orbits or shells.

• Each orbit is a certain distance from the nucleus and contains a definite number of electrons.

• The orbits are filled in a routine way:– First orbit: 2 electrons– Second orbit: 8 electrons– Third orbit: 8 electrons

Bohr model of Nitrogen:

• Check your periodic table for Nitrogen

N7 -3

Nitrogen

14.0

Bohr model for Magnesium:

Bohr Model for Argon

Isotopes

• Atoms of the same element that have different numbers of neutrons

• Two ways to recognize isotopes:1. Isotope Name: Chemical name – mass #

– Example: Carbon -11, Carbon -12, Carbon -13

2. Isotope Symbol:

• Example:

Mass number

atomic numberX

Chemical Symbol of element

Isotopes:

• The Isotope symbol makes it easy to find the number of neutrons

Atomic mass:

• The weighted average of the mass an element’s naturally occurring isotopes.

• A “weighted average” means you take into account the % of each isotope that is present in an ordinary sample of the element.

Example:

A particular sample of carbon has 10% carbon-11, 80% carbon-12, and 10% carbon-13. Calculate the atomic number of this sample of carbon.