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8th Chemistry of Matter Part I
Chapters 14 & 15
Notes Page
History of Atoms
Demo: Aluminum Foil
All material is made of particles, named atoms “cannot be divided”
Scientists came to realize that all matter is made up of elements. An
element is matter made of atoms of only one kind.
Example: iron is made up of iron atoms.
Democritus – Greek philosopher 440BC. Particles or smallest pieces cannot
be divided any further. Atomos – “uncuttable”.
John Dalton – English schoolteacher, early 19th century
His idea about matter;
1. matter is made up of atoms
2. atoms cannot be divided into smaller pieces
3. all atoms of an element are exactly alike
4. different elements are made of different kinds of atoms
He thought an atom was pictured as a hard sphere, that was the same
throughout, something like a marble pg. 405 Figure 3
William Crookes, English scientist, 1870 did experiments to test Dalton’s
theory. He developed a cathode-ray tube or CRT. He discovered that atoms
have an Anode, which has a positive charge. He also discovered that atoms
have a Cathode, which has a negative charge,
J.J. Thomson, English physicist, 1897, he discovered that opposite charges
attract each other. He named the negative Cathode charge, electron. He
thought an atom was pictured as a ball of modeling clay with ball bearings
mixed though. Pg. 408, Figure 8. He stated the positive charge of the clay is
equal to the negative charge of the electrons. Therefore, the atom is
neutral.
Ernest Rutherford, 1906, discovered the positive charge of an atom which
he called a proton was crammed into a small space in the middle of the atom,
which he called the nucleus. He said the rest of the atom is empty space
occupied by the atom’s smallest part, the almost massless electron.
Twenty years later scientists discovered by using more modern experiments
that atoms have neutrons in the nucleus that have a neutral charge.
Pg. 411, Figure 13
Neils Bohr, physicist, twentieth century, he said that electrons will move
around the nucleus, much like the moon orbiting around the Earth
Later a new model of the atom was made, showing an electron cloud that
electrons are constantly moving around in while the proton and neutron stay
together in the nucleus. It was also determined that the electrons are more
likely to be close to the nucleus rather than farther away because they are
attracted to the positive charges of the proton. Pg. 413, Figure 15
Facts about atoms:
1. A sheet of paper is about 10,000 atoms thick.
2. There are 2,000 billion billion atoms of oxygen in one drop of water –
and twice as many atoms of hydrogen.
3. Newspaper pictures are made from tiny dots of ink. Each dot contains
about a billion billion atoms!
Atoms of different elements contain different number of protons.
The protons and neutrons stay together due to a strong nuclear force.
The smallest of the atoms, the hydrogen atom has one proton in its nucleus.
The heaviest of the atoms, Uranium, has 92 protons.
When different elements are combined together a new element can be
formed by the number of protons, neutrons and electrons changing positions.
This can also change the charge of the element from positive to negative to
neutral. This process creates energy and is called radioactive decay.
When a proton leaves the nucleus and element changes into another element
it is called transmutation.
Loss and Gain of Particles;
Alpha Particles – two protons and two neutrons undergo transmutation. This
creates nuclear radiation.
Beta Particles – a neutron becomes unstable and splits into a proton and an
electron. The electron is released with a large amount of energy. The proton
stays in the nucleus.
Sharing of Particles;
Metallic bonding – metal atoms share their pooled electrons.
Covalent bond – a chemical bond between nonmetal atoms who share
electrons. This forms a neutral particle with the same number of negative
and positive charges. This new particle is called a molecule.
Different Types of Elements
Isotopes – atoms of the same element that have different number of
neutrons. Pg. 415, Figure 16
Compound – is a pure substance containing two or more elements that are
chemically bonded, ionic bond.
Ion – an atom that is no longer neutral because it has lost or gained an
electron.
Molecule – compound that shares electrons.
Periodic Table of the Elements
Dmitri Mendeleev (men duh LAY uhf), Russian chemist, 1869, published the
first version of the periodic table. Pg. 434, Figure 1. He arranged the
elements in order of increasing atomic mass and saw a pattern.
Atomic mass unit (amu) – measures the particles in an atom. The mass of a
proton or neutron is about 1 mass unit. Example: Hydrogen 1.008
Elements with similar properties fell into groups on the table.
Henry Moseley, English physicist, early twentieth century arranged periodic
table according to atomic number instead of mass.
Atomic number – number of protons in elements.
Modern day Periodic Table
Period – row of elements whose properties change gradually and predictably.
Are labeled 1 – 7
Group – contains elements that have similar physical or chemical properties.
Columns 1 – 18
Two sections –
Representative elements - section 1, groups 1-2 & 13 -18
Transition and Inner transitions elements – section 2, groups 3 – 12
Assignment:
#2 Families (Groups) of the Periodic Table
Pgs. 436 – 437
Atoms By The Numbers – Bohr Chart
Many atomic nuclei are stable when they have about the same number of
protons and neutrons.
Example; Carbon – 12 is the most stable isotope of carbon because it has 6
protons and 6 neutrons.
Some nuclei are unstable because they have too many or too few neutrons.
This causes repulsion to build up, the nucleus must release a particle to
become stable. This will release energy called radioactive decay. This can
also change the identity of the element.
Assignment #3
Go over together, front page
Examples on board;
Students do back page independently
Parts of an Atom
Assignment #4
Go over together, front page
Examples on board; backpage Bohr Models
Electron Dot Diagram and the Ocet Rule
Do front page together
Examples on board – show whether to add or subtract according to octect
rule