Atoms and Molecules

1
Atoms and Molecules

• Atom is smallest particle that can be identified
  as a particular substance.
• Molecule is two or more atoms bonded to each
  other.

2
Elements

• Around 110 different elements have been
  identified. Of these around 80 are found in
  nature on Earth.
• Most common element on Earth is oxygen, symbol O.
• Most common element in universe is hydrogen,
  symbol H.

3
Symbols

• Symbols are shorthand for the name of the
  element.
• Usually first one or two letters of name.

4
Atoms

• Atom is the basic unit of an element. Atoms
  contain protons, neutrons, and electrons.
• Protons positive charge (1)
• Neutrons neutral, no charge
• Electrons negative charge (-1)

5
Nucleus

• Contains protons and neutrons.
• All positive charge of atom is in nucleus.
• Majority of mass is in nucleus.
• Protons have mass of 1 amu.
• Neutrons have mass of 1 amu.

6
Electrons

• Mass is about 1/2000 of the mass of a proton.
• Electrons orbit the nucleus similarly to planets
  orbiting the sun.
• All negative charge of the atom is due to
  electrons.

7
Charge of the atoms

• Elements have no net charge.
• The number of protons equals the number of
  electrons.

8
The Subatomic Particles

• Proton the identity particle. The number of
  protons in the nucleus determines which element
  the atom is.
• Neutrons a neutral particle
• Electrons the personality particle. The
  electrons give the atom its characteristic
  behaviors.

9
The Symbol Box

• The Atomic Number usually at top of box. Is
  the number of protons in the nucleus.
• In an element, the atomic number is also the
  number of electrons.
• The Symbol shorthand for name.
• The Atomic Mass usually at the bottom of box.
  Is the sum of the protons and neutrons.

10
Masses

• AMU atomic mass unit. 1.67 x 10-24 g
• Proton and neutron 1 AMU
• Election mass 9.11 x 10-28 g
• Carbon atom mass 12 amu

11
Gain/Loss of Electrons

• Atoms can gain from other atoms or lose electrons
  to other atoms.
• An atom that loses an electron has a net positive
  charge because there are more protons than
  electrons. Remember the atom started with equal
  numbers of protons and electrons.
• An atom that gains an electron has a net negative
  charge because there are more electrons than
  protons.

12
Ions

• When an atom has lost or gained an electrons it
  is called an ion.
• Ions with positive charge are known as CATIONS
• Ions with negative charge are known as ANIONS

13
The Periodic Table

• An organized table of all known elements.
• To the left of the stairstep are metals
• To the right of the stairstep are nonmetals
• Along both sides of the stairstep are metalloids.
• Rows are known as periods
• Columns are known as groups

14
Neutrons

• Isotopes
• To be a particular element, an atom must have a
  specific number of protons, i.e. 8 protons are in
  an oxygen atom.
• Most commonly an oxygen atom has 8 neutrons.
  Sometimes the nucleus contains has a different
  number of neutrons. Isotope is the term for
  atoms of a single element that have different
  numbers of neutrons.

15
Specifying an Atom

• See paper on symbols on
• www.drbillboyle.com