chem: ch 2

  • Element: pure substance that can’t be broken down into 2+ simpler substances by chemical process

    • contains 1 type of atom only

    • can be atom/molecule

  • Compound: pure substance containing 2+ elements that are chemically combined

    • molecule/ionic compound

  • Mixture: made of 2+ substances that aren’t chemically combined

Atom

  • its total charge is neutral

  • has the same number of protons and electrons

  • consists of subatomic particles

    • protons and neutrons in the nucleus

    • electrons orbiting the nucleus

proton

electron

neutron

relative mass

1

1/1840

1

relative charge

1+

1-

0

symbol

p

e

n

Periodic Table

  • atomic number: number of protons/electrons

    • aka proton number

  • mass number: protons + neutrons

    • aka relative atomic mass, or nucleon number

  • group: number of valence electrons

    • vertical

  • period: number of electron shells

    • horizontal

Groups

  1. Metals (Group 1-2)

  2. Halogens (Group 7)

    • means “salt former”

    • react with metals to form ionic salt

  3. Noble gases (Group 8)

    • have full outer shells, which make them unreactive

    • don’t lose/gain/share electrons

    • exist as monatomic elements