SUMMARY

Session Goals

• Define key terms relating to structure of matter

• Describe the Bohr model of the atom

• Outline the basic properties of fundamental subatomic particles

• Differentiate between atomic number and atomic mass number

• Differentiate between elements, compounds, and mixtures

Bohr Model of the Atom

• An approximation of quantum mechanics

• Referred to as the ‘planetary’ or ‘solar system’ model

Structure of the Atom

• Nucleus: Dense central area containing protons and neutrons

• Orbitals: Regions around the nucleus where electrons travel; each has a specific radius and maximum electron capacity

More about Orbits

• Electrons in each orbital have specific energy levels based on their location

Fundamental Particles

• Neutron (n): Charge 0, mass 1 amu

• Proton (p+): Charge 1+, mass 1 amu

• Electron (e-): Charge 1-, mass ≈ 1/1837 amu

Numbers of Particles in an Atom

• In neutral atoms, the number of electrons equals the number of protons

• Number of neutrons is often equal to or varies relative to the proton count

Elements

• Defined as a substance made of one type of atom (same proton number)

• Smallest unit is the atom; identified by atomic number (Z)

• Isotopes are different nuclear forms of an element with varying neutron numbers

Examples of Elements

• Hydrogen (H): Z = 1, 1 orbital electron, most common isotope has 0 neutrons

• Calcium (Ca): Z = 20, 24 isotopes with 40Ca being the most abundant naturally occurring isotope

Compounds

• Comprise two or more different elements chemically bound; differ in properties from constituent elements

• Requires chemical means to break down

Mixtures

• Combinations of elements without chemical bonding

Molecules

• Groups of two or more atoms bonded with shared electrons, having no net charge

• Smallest unit of a compound retaining its chemical properties