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Exams semester 2 year 9: Science (Techtonic plates (Definitions (Magnetic…
Exams semester 2 year 9: Science
Chemistry
2.1 - Atoms
Atoms are so small you need a special microscope to see them.
118 types known, 98 occur naturally on earth, 20 made in labs
Atoms in compounds/elements
Atoms can either combine with other atoms to form clusters of atoms known as molecules or form large grid-like structures known as crystal lattices.
In molecular elements, each molecule is made of just one type of atom.
If a substance is made up of just one type of atom, it is an
Element
. If a substance is made of multiple types of atoms, it is a
Compound
.
Atoms have subatomic particles that are the building blocks of atoms.
Protons (+)
Electrons (-)
Neutrons (N/A)
Protons
and
neutrons
exist inside the
nucleus
of the atom, while
electrons
orbit the nucleus.
Protons and neutrons are
1800x heavier
than electrons
Although each electron is 1800 times lighter than a proton, the electron clouds can be 100 or even 1000 times larger than the nucleus. This means that if the nucleus were the size of a golf ball, the electrons would form clouds the size of a football stadium and the electrons would be the size of a single grain of sand. It also means that most of an atom is empty space.
Negative (-) and positive (+) charges attract, so electrons are pulled towards the nucleus. This happens just enough to keep them with the atom, but not enough to pull them into the atom completely.
Atoms have no charge because electrons=protons
Atomic number and mass number
The number of protons in the nucleus determines what type of atom it is, for example all oxygen atoms have 8 protons in the nucleus
This number is called the atomic number
There is a way atoms can be written that shows the mass number or atomic mass (different), the atomic symbol and the atomic number.
The Atomic Mass
is the average mass of all elements of that type, and it changes between elements because the number of neutrons can change.
The Mass Number
is the mass of a particular atom of the element and is equal to the number of
protons
(the atomic number) + the number of
neutrons
.
Ions
Cations +
-ate
Anions -
-ide
Atoms with more or less electrons. Lose them, positive charge, gain them negative charge.
2.2 - Metals, Non-Metals and Metaloids
Metaloids
Act like non-metals in most ways
Semi-conductors, which means they can conduct electricity under certain conditions
Non-Metals
Brittle
Poor conductors
Dull
Often have low melting and boiling points
Metals
Shiny
Lustrous
Ductile
Malleable
Conductors
Pure metals are nor that strong, alloys, or impure metals mixed with others are stronger
Periodic table
Horizontal lines are called periods
Vertical lines are called groups
5.4 Electrons are arranged in shells
Bohr model describes this
The valence shell is the outermost shell
First 20 elements limit of electrons per shell are in this order 2, 8, 8, 2
Groups often indicate the number of electrons in the valence shell, while periods indicate the number of valence shells
One proof of electron shells is the emission spectrum of atoms, where light is given off after heat is added to a substance, and the electrons all jump one shell further out. The emission spectrum of each atom is unique
Isotope
Radioactive isotopes exist because they have too much mass.
Carbon has three isotopes, Carbon12, Carbon13, Carbon14.
Atoms that have more or less neutrons
RAM or relative atomic mass is the average mass of all elements of that type. For example, Carbon 12 is the most common isotope of carbon, so the atomic number being an average of all carbon atoms is 12.0107
RAM = (atomic mass of isotope 1 x abundance of isotope 1) + (atomic mass of isotope 2 x abundance of isotope 2) also add as many isotopes as there are
RAM of Carbon = (12x0.9893) + (13 x 0.01109) + (14 x 0.000000000001) = 12.01577 (not quite atomic mass numbers must be a bit off)
Techtonic plates
Crust
Continental crust (Land) Lighter
Oceanic crust (Ocean) Denser
Types of plate boundaries
Converging - Plates are colliding with each other (Faster plate sub ducts under the other
Diverging - Plates are moving away from each other
Transform boundaries - Where the plates are sliding past each other
Definitions
Magnetic stripping: patterns of magnetism trapped in rocks on each side of plate boundaries
Ocean Trench: a deep channel in the ocean floor where crust is sinking downwards:
Rifting: the process of continents breaking up, subsiding and allowing in water from the sea
Asthenosphere: a layer of ‘plastic’ semi-solid rock in the mantle
Theories of continental drift
Continental drift is the idea that continents are continually moving and have change position significantly
Evidence: the continents fit together
The theory of sea-floor spreading proposes that the middle of the ocean is spreading. Moving slowly moving in opposite directions
Proposed by Harry Hess
Mid atlantic ridge is evidence
Both theories explain earthquakes, mountains and deep sea trenches.
Alfred wegener
Put the idea of continental drift into a book and also named the theory
He proposed the continents once fitted together and called this mega continent pangea
Pangea is supercontinent that existed 220 million years ago
It started to break up and the continents drifted apart
Evidence for pangea
Similar fossils
Coastlines fit together
Rocks and landforms
Earth has a solid core
Earths core is made of 4 things
Mantle
Inner Core
Crust
The crust is broken into tectonic plates.
The plates float on top of the semiliquid magma.
Sometimes the plates crash into each other, causing a plate to slide under the other.
The plate on top buckles and pushes the land upwards.
Outer Core
Plates
Lithosphere
100km thick
Less dense than the material below it so it floats
Crust and upper mantle
Athenosphere
Plastic layer below the athenosphere
The plates of the lithosphere float on the asthenosphere
