Review of Atomic Model

Key Words

subatomic particle energy levels

atomic mass proton isotope

electron neutron ion

atomic mass unit (u) atomic number

Elements are pure substances containing one type of atom – found on the Periodic Table.

The atom is the smallest part that retains all the properties of that element.

protons (p+) neutrons (no) electrons (e-)

Charge

Mass

Location

+1.6 x 10-19 C 0 -1.6 x 10-19 C

1.67 x 10-24 g 1.67 x 10-24 g 9.11 x 10-28 g

Nucleus Nucleus Orbit clouds

The atomic number (Z) is the number of protons in the nucleus of an atom - identifies an element.

The atomic mass (A) is the number of protons plus the number of neutrons.

H : the hydrogen atom

H+ : a positively charged hydrogen ion H- : negatively charged

hydrogen ion

Ion: an atom that has gained or lost electrons.

Results in a negative or positive charge equal to the electrons transferred.

Neutral: an atom with the same number of protons and electrons – cancelled charges.

Deuterium Atomic Mass = 2

Atomic Number = 1

Hydrogen Atomic Mass = 1

Atomic Number = 1

Isotopes: Atoms with the but a different number of neutrons.

Atomic mass is actually an average of isotopes of an element based on relative abundance in nature.

same number of protons

Mass spectrometer determines the mass of individual atoms or isotopes.

Sends atoms through a magnetic field which bends their paths.

The heavier the atom – the less it bends.

Potassium isotopes:

1. 19 protons and 20 neutrons - mass number of 39(potassium-39 39K)

2. 19 protons and 21 neutrons - mass number of 40 (potassium-40 40K)

3. 19 protons and 22 neutrons - mass number of 41 (potassium-41 41K)

Magnesium exists as three isotopes in the world:

78.99% is 24Mg (23.985 μ)10.00% is 25Mg (24.986 μ)11.01% is 26Mg (25.982 μ)

(0.7899)(23.985 μ) = 18.95 μ

(0.1000)(24.986 μ) = 2.499 μ

(0.1101)(25.982 μ) = 2.861 μ

= 24.31 μ +

Calculate the average atomic mass of magnesium:

helium 5He 6He

The nucleus of some isotopes are unstable and break apart over time - radioactivity.

Radioisotopes - unstable nuclei releasing energy and/or particles.

Release of energy is called radioactive decay.

Atom may be converted into another isotope or a completely different element.

Half-life - amount of time it takes for half the radioisotope to be converted into another particle.

Many different types of decay: alpha decay, beta decay, gamma decay

• Isotopes - differ in mass because they have different numbers of neutrons.

• Relative / percent abundance is the fraction of each isotope found in an average sample of the element.