Chemistry - Atoms and the periodic table

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Atom

• consists of a dense nucleus and cloud of electrons that move around the nucleus

Compounds

• Two or more of the different atom

Molecules

• Two or more of the same atom

Nucleus

• a cluster of two sorts of particles

  • Protons (positively charged)

  • Neutrons (no charge charged)

What do the electrons do?

• circle around the nucleus

Relationship of when an atom is in its neutral state

Number of Protons = Number of Electrons

Atom Diagram

>(mentally rehearse)

The symbols, charges, sizes relative to a proton, and mass (kg) of Protons, Neutrons, and Electrons

Electrons

• Negatively charged

• Held by electrostatic attraction

Protons (atomic number)

• Positively charged

• Determines the type of element through the atomic no. (no. of protons)

• Hydrogen always has 1 proton

• Helium always has 2 protons

Neutrons

• No charge

• Combined with the protons, they determine the atomic mass of an element

• Each element can have the same protons but different no. of neutrons.

Element layout on the periodic table

^(Helium)

Atomic number

• The number of protons in an atom

• Atoms are electrically neutral and so there must be the same number of electrons
  as protons. In any atom:

• atomic number = number of protons = number of electrons

Mass number

• The total number of particles in the nucleus (protons + neutrons together)

• Neutrons do not add any charge to an atom, so there is no strict rule connecting them with protons or electrons.

• mass number = number of protons + number of neutrons