Atomic StructureAtomic Structurelecture 4.1lecture 4.1

Atomic structureAtomic structureSmall, dense nucleusSmall, dense nucleus

Protons: (+) chargeProtons: (+) charge

Neutrons : (0) no chargeNeutrons : (0) no charge

Electrons: (-) chargeElectrons: (-) charge

# Protons = # electrons# Protons = # electrons

Electrically neutral, as + and Electrically neutral, as + and – charges are equal– charges are equal

Particle sizesParticle sizes

Almost all the mass is in the nucleus (Almost all the mass is in the nucleus (Protons + Protons + Neutrons )Neutrons )

Electrons move in a cloud around the nucleusElectrons move in a cloud around the nucleus

If the nucleus was the size of a If the nucleus was the size of a marblemarble, the electron , the electron cloud would be the size of a cloud would be the size of a stadium!stadium!

Energy levelsEnergy levels

Electrons fill up Electrons fill up orbitals around the orbitals around the nucleusnucleus

Each level holds only Each level holds only so many electronsso many electrons

Level 1- holds 2Level 1- holds 2

Level 2 – holds 8Level 2 – holds 8

Level 3 – holds 18Level 3 – holds 18

Left side: If an atom had its first 2 orbitals filled how many electrons and protons would it have?

Valence electronsValence electrons•the electrons on the outermost level are called the electrons on the outermost level are called valence valence electronselectrons, determine reactivity, determine reactivity

•ReactivityReactivity is how likely an atom is to form bonds with is how likely an atom is to form bonds with another elementanother element

Left side: How many valence electrons do Ar and H have?

IsotopesIsotopes

Isotopes are variations of the same elementIsotopes are variations of the same element– The proton number is always the same, but The proton number is always the same, but

the number of the number of neutronsneutrons can change can change– They have a different atomic mass. They have a different atomic mass.

The greater the number of neutrons the The greater the number of neutrons the greater the mass greater the mass

Calculating neutronsCalculating neutrons

Mass # – atomic # = # neutronsMass # – atomic # = # neutrons

Average atomic mass :Average atomic mass :Numbers are the Numbers are the averageaverage masses masses of all the of all the isotopesisotopes of the element of the element

Summary Review

1. What are the 3 subatomic particles, their charge, and location?

2. If an element has 2 protons how many electrons does it have?

3. The electrons in the outermost energy level are called ____________ electrons.

4. What is an isotope and what is atomic mass?