Unit 3 Elements, Atoms, and Ions
(Oh My!)
Chpt 3 Elements, Atoms, and Ions
Chpt 11 Modern Atomic Theory
Alchemical History
• In ancient times, it was believed that there were only 4 elements:
earth, wind, fire, water
• https://www.youtube.com/watch?v=Gs069dndIYk
• In the middle ages, alchemists attempted to create gold, the
philosopher’s stone, or the elixir of life from natural materials.
• Dangerous “experiments”
• Recorded “symbols” of
elements
What are elements?
• Elements are made of one type of atom
• Presently, there are 118 (both naturally occurring
and man-made) and most are metals
• Synthetic elements (>93) have very short
lifespans from days to seconds
• Little known facts:
– the first element made after the Big Bang was
hydrogen, which is also the most abundant in the
universe
– oxygen is the most abundant in the earth and the
body
– all living forms of matter (organic molecules) are
made of carbon
Natural States of Elements
• Most elements exist in their “pure elemental”
form as a collection of single atoms
• 7 elements exists as diatomic molecules in
their natural state
– hydrogen, H2
– nitrogen, N2
– oxygen, O2
– fluorine, F2
- chlorine, Cl2
- bromine, Br2
- iodine, I2
Element Name and Symbols
• Elements are named after their physical
properties, scientists, countries/place
• Rules for symbols
– Always capitalize the first letter
– some symbols come from their original Greek, Latin
name
Chemical formulas for molecules and
compounds
• Formulas are shorthand for the name of the
molec/cmpd
• Represents the number of atoms for each
element in the cmpd
– H2O = 2 hydrogen atoms, 1 oxygen atom
– C6H12O6 = 6 carbon atoms, 12 hydrogen, 6 oxygen
atoms
• ALWAYS use subscripts for the number
• “1” is implied – do not write it
History of atomic theory
• Law of Constant Composition – compounds
always have the same ratios of elements
regardless of their source
– H2O = 2:1
– H2O2 = 2:2 = 1:1
– CO2 = 1 : 2
Dalton’s Atomic Theory (DAT)
LoCC made John Dalton think about what made up
elements….
1. Elements are made of atoms.
2. All atoms of a given element are identical.
3. Atoms of a given element are different from
those of any other element.
4. Atoms of one element can combine with atoms
of other elements to form compounds.
5. Atoms cannot be separated by any means.
Thomson and the Plum Pudding Model
• 1897 – J.J. Thomson discovered the electron
• Used a cathode ray tube
• It proved that atoms are made of negatively charged particles,
which he called “electrons”. Their negative charge was balanced
by the overall positive charge of the atom. This made the whole
atom neutral made of empty space.
• Plum Pudding (or chocolate chip cookie)
Ernest Rutherford and Gold Foil
Experiment
• Early 1900s Ernest Rutherford (and Co.) discovered the proton
• Gold foil experiment
• It proved that atoms contained a center of positive charge,
which he called the “nucleus” filled with “protons”, or
positively charged particles. The nucleus was surrounded by
electrons.
Neils Bohr model
• 1915 Neils Bohr theorized that electrons travel
on orbits around the nucleus. The orbits have
specific amounts of energy, or quantized
energy. Electrons can jump orbits by
absorbing or emitting energy. When electrons
emit energy, they throw out a photon, or light
particle.
• Ground state electron –
lowest energy level
• Excited electron –
higher energy level
• As an excited electron
falls back down to its
ground state, it emits a
photo
James Chadwick
• 1920s, James Chadwick discovered the
neutron
• Bombarding heavy particles at atoms
• It proved that atoms contained neutral
particles in addition to protons and electrons.
It accounted for the rest of the atom’s mass.
Atomic Structure Summary
• Made of mostly empty space with a nucleus at
center
• Atoms contain 3 subatomic particles:
– protons – positive charge, located in nucleus
– neutrons – no charge, located in nucleus
– electrons – negative charge, move around nucleus
• Protons and neutrons make up the atom’s mass
(atomic mass)
• Number of protons identify the atom (atomic
number)
• A neutral atom has the same number of protons
and electrons
Isotopes
• Not all atoms of a particular element are identical
• Isotopes – atoms of a given element that have a
different atomic mass (different number of
neutrons)
• For carbon
– C-12 (6 protons, 6 neutrons)
– C-13 (6 protons, 7 neutrons)
– C-14 (6 protons, 8 neutrons)
• Use AZX notation
– A – atomic mass
– Z – atomic number
– X – chemical symbol
Ions
• When atoms lose or gain electrons, they
become charged, called ions
• Ions can be positive (+) or negative (-)
• Cations are positive ions, electrons lost
• Anions are negative ions, electrons gained