Science 10 Unit A: Chemistry
Part 1: Matter and the Periodic Table
Properties of Matter:
Some attempts to define - matter:
- has mass and takes up space
- is composted of atoms/particles
Classification of Matter
Pure Substances: ·all the particles that make up the
substance are identical
·e.g. elements and compounds
Mixtures: combinations of pure substances.
J.J. Thomson: Raison Bun Model
- it consists of a 'bun' made
of positive charge and
'raisins' made of electrons
- the electrons are stuck in
the bun and do not move
Niels Bohr: Bohr Model
- electrons can occupy many orbitals
- electrons jump up an orbital when
energy (light) is absorbed.
- electrons jump down a level when
energy (light) is released.
Success – Thomson discovered the
electron using the charge to mass ratio
experiment. He recognized that the
positive part of the atom must be larger
than the negative part.
Success – explains why hot objects
produced certain colours of light and
allows electrons to move between
orbitals.
Failures: Electrons are not fixed, but
free to move. What about protons?
Early Models of the Atom:
Dalton: Billiard Ball Model
- atoms are tiny, indivisible spheres
- elements are made up of atoms
- atoms of one element are the same, atoms of
different elements are different
- atoms of one element can combine with other
elements to form compounds
- atoms cannot be created, divided into smaller
particles or destroyed in the chemical
processes.
Success – explained conservation of matter: atoms
are not created or destroyed in a chemical reaction,
just rearranged.
Failures: Atoms are not indivisible.
Ernest Rutherford: Planetary Model
- Rutherford conducted the Gold Foil
Experiment
- model has a dense, positive charge in
the middle (nucleus) and smaller
electrons orbiting around the centre.
Success – Created the nucleus with
positive charge inside and negative
charge outside.
Failures: Electrons don’t move in
circles and they are not fixed in one
orbital.
Failures: model only worked for
hydrogen and electrons don’t stick to
set paths…
Current Model: Quantum Model
Quantum theory predicts that we cannot know the
exact location of the electron at any given time.
We can only calculate the probability of it
being somewhere. Electrons travel around the
nucleus in a probability cloud.
Success – explains and lead to LASERs, the
microchip/transistors, the electron microscope,
MRI machines.
Failures: proposes some weird ideas about the
universe…no one really understands it.
Practice: Matter
Practice (Ref. pg 14
of text)
Your Periodic Table
One way to draw a simple diagram of an atom is to
show its protons and neutrons in an electron orbital
diagram.
The elements are arranged into three main categories:
- metals (left of staircase)
- non-metals (right of staircase)
- metalloids (along staircase)
The table is arranged into groups (up and down) and
periods (left and right).
Other groups also exist: Alkali Metals (group 1),
Alkaline Earth Metals (group 2), Halogens (group 17)
and Noble Gases (group 18). Noble gases do not
usually react with other elements.
Note: helium has two electrons in its orbital. At atom
can have at most two electron in the first orbital. Now,
let’s look at neon:
The outer orbital in an atom is called the valence
orbital. Electrons for the first 20 elements fill orbitals
in a set pattern:
Mass Number (Atomic Mass)
The mass number is the sum of the protons and
neutrons in an atom.
Atoms that have a different number of neutrons than
protons are called isotopes.
Iona
An ion is an element that has gained or lost electrons
to become more stable. Elements are more stable
when their valence orbital is filled according to the
pattern above. Positive ions are called cations,
negative ions are called anions.