This is all the content required for Chemistry paper 1. Each topic/lesson subheading has a link to either a cognito or Free Science lessons video. This doc states if the topic is triple content. Also includes required practicals.
Chemistry paper 1 videos notes
ATOMIC STRUCTURE AND THE PERIODIC TABLE
Atoms and ions:
- Each atom is made up of smaller particles. Its basic structure is a centre nucleus
surrounded by electrons which orbit around the nucleus in shells.
- The nucleus is made up of protons and neutrons.
- Protons = relative mass of 1, +1 charge
- Neutrons = relative mass of 1, 0 charge
- Electrons = relative mass 2000 x smaller which is often very small, -1 charge.
- Atoms are mainly empty space.
- In every atom there is the same number of protons and electrons and the positive
and negative charges cancel each other out so the atom stays neutral.
- Atoms can lose or gain electrons so the atom is no longer balanced and the overall
atom would become charged. We then call this an ion. For example if an atom
gained an extra electron, it would become a negative ion because there are more
electrons than protons. However if an atom loses electrons, then it becomes a
positive ion as there are more protons.
- That atomic number tells us how many protons the atom has and the mass number
tells us the sum of the protons and neutrons.
- Atoms are very small, having a radius of about 0.1 nm (1 x 10-10 m).
- The radius of a nucleus is less than 1/10 000 of that of the atom (about 1 x 10-14 m).
Elements, isotopes and relative atomic mass:
- The number of protons determines the element. The number of neutrons varies
between the individual atoms of an element. As long as the number of protons
remains the same, it’s still the same element and these different forms of that
element are called isotopes.
- Isotopes are different forms of the same element that have the same number of
protons but different numbers of neutrons.
- Relative atomic mass:
(isotope abundance x isotope mass) + (isotope 2 abundance x mass)/100
Or abundance % x mass number + abundance % x mass number/100
Compounds, molecules and mixtures:
- Molecules are groups of 2 or more atoms that are held together by chemical bonds.
For example, oxygen.
- Compounds contain 2 or more different elements held together by chemical bonds.
For example water would be a compound because it contains the elements hydrogen
and oxygen.
- Mixtures are 2 or more substances not chemically combined together, so they
haven't reacted together.
History of the model of the atom:
- John Dalton described atoms as solid spheres and different types of spheres might
make up the different elements.
- JJ Thomson came up with the Plum Pudding model. This shows that the atom is a
ball of positive charge with negative electrons embedded in it.
- Rutherford took positively charged alpha particles and they fired them at a thin sheet
of gold. If the positive charged gold atoms were spread out, then the alpha particles
, should go straight through. However some of the alpha particles were deflected to
the side and a small number deflected back. Rutherford then suggested the nuclear
model that there is a nucleus which contains all the positive charge and negative
charge is like a cloud around the nucleus.
- Bohr discovered that the electrons orbit the nucleus in shells.
- Further experiments by Rutherford suggests that the positive charge in the nucleus is
made up of small particles called protons.
- Chadwick then discovered neutrons.
Electron arrangement:
- In order for atoms to be stable, they need to have a full outer shell. If they don’t then
they have to react with another atom to gain or lose electrons that they need.
- If the atom lost 2 electrons, it would form a 2+ ion but if it gained 2 electrons then it
would become a 2- ion.
Development of the periodic table:
- Before the discovery of protons, neutrons and electrons, scientists attempted to
classify the elements by arranging them in order of their atomic weights. However
this meant some elements were placed into the incorrect groups since chemical
properties were ignored if the strict order of atomic weights was followed.
- Mendeleev overcame some of the problems by arranging elements in columns based
on their similar properties. He arranged elements horizontally in order of atomic
weight but left gaps for elements that he thought had not been discovered. In some
places he changed the order of atomic weights to maintain the pattern. Overtime
gaps were filled in with new elements.
- Elements with properties predicted by Mendeleev were discovered and filled the
gaps. Knowledge of isotopes made it possible to explain why the order based on
atomic weights was not always correct as it explained why some atoms had heavier
atomic masses than expected..
Modern periodic table:
- Elements are arranged in order of increasing atomic number which represents the
number of protons in the atoms of that element.
- The elements in each vertical column (group) have similar chemical properties. This
is because they have the same number of electrons in their outer shell. This is what
determines how an element reacts.
- Group 1 elements are called alkali metals which all have one electron in their outer
shell. They all react violently with water. They also get more reactive as you go down
the group.
- Group 7 elements are called halogens which all have 7 electrons in their outer shell.
These become less reactive as you go down the group.
- Group 0/8 are called noble gases which all have full outer shells. Because they don’t
need to gain or lose any electrons, the noble gases are all unreactive.
Metals and non-metals:
- In the periodic table, we see there are much more metals than nonmetals. Metals
form positive ions when they react. Whereas nonmetals don’t form ions or they form
negative ions.
- All metals have metallic bonding, they are malleable (bend), nearly all of them have
high melting and boiling points.
- Nonmetals are dull in colour, brittle, low melting and boiling points.
Group 0:
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