Atoms: Basic Building Block of Matter

• Atoms are the smallest unit of an element.

• An atom of one element can’t be changed into another element

• Every atom of an element has the same number

Atoms: Law of Conservation of Matter

• Matter cannot be created or destroyed, only rearranged

• Atoms follow the LOC of Matter. You cannot destroy atoms, only combine or separate from other atoms

Atoms

• Atoms are made of subatomic (sub = lower/smaller) particles called:

  • protons

  • neutrons

  • electrons

Protons

• Positively charged

• Located in the nucleus

• Mass is 1 AMU (atomic mass unit)

• The number of protons determines the type of element on the Periodic Table

Neutrons

• Neutrally charged

• Located in the nucleus

• Mass is 1 AMU (atomic mass unit)

Electrons

• Negatively charged

• Located in the electron cloud (surrounds the nucleus)

• Have almost no mass

Subatomic
Particle

Type of
Charge

Location

Atomic
Mass Unit

Proton

Positive

In the
Nucleus

1 AMU

Neutron

Neutral

In the
Nucleus

1 AMU

Electron

Negative

Outside the
Nucleus

0 AMU

Label an Atom

Label an Atom

​Electron

​Neutron

​Proton

Atoms

• # of protons = # of electrons in a neutral atom (think of zero pairs)

• neutrons do not affect the overall charge of an atom (because they are neutral)

• protons + neutrons determines the mass of an atom

  • the mass is found in the nucleus

Atomic Mass vs Atomic Number

• atomic mass = # protons + # neutrons in an atom

• Example: Find the mass of an atom with 12 protons and 12 neutrons

  • 12+12 = 24

• atomic number = number of protons OR number of electrons in a neutral atom

  • all atoms will be neutral in this class