C1 - Atomic Structure and The Periodic Table Flashcards
What are all substances made out of?
Atoms
What is the estimated radius of an atom?
0.1 nanometres
Where is the nucleus in the atom?
In the middle
What is the nucleus made up of?
Protons and neurons
What is the estimated radius of a nucleus?
1x10^-14m
What is the charge of a nucleus?
Positive
How much of the atoms mass is in the nucleus?
Nearly the whole mass
Where are the electrons in the atom?
Around the nucleus in electron shells
What charge are electrons?
Negative
How much mass do electrons have?
Virtually none
What determines the size of an atom with electrons?
Their orbit
What charges are atoms?
Neutral
Why are atoms neutral?
They have the same amount of protons as electrons. Therefore they cancel out the charge
What is an ion?
An atom or group of atoms that has lost or gained electrons. For example, an ion with a 2- charge would have 2 more electrons that protons
What does the nuclear symbol of an atom tell you?
The atomic proton number and mass number
Atomic number
Tells you how many protons there are
Mass number
Tells you the total number of protons and neutrons in the atom
How can you get the number of neurons from the nuclear symbol?
Atomic number - mass number
What is an element
A substance made up of atoms that all have the same number of protons in their nucleus
Isotopes
Different forms of the same element, which have the same number of protons but a different number of neutrons. So they have the same atomic number but different mass numbers
What is used if there are too many isotopes for a single element?
They use a relative atomic mass which is an average mass taking into account the different masses and abundances of all the isotopes that make up that element
Relative atomic mass (Ar) formula
sum of (isotope abundance x isotope mass number) / sum of abundances of all isotopes
Compounds
Substances formed from 2 or more elements, each are in fixed proportions throughout the compounds and held together by chemical bonds
How are bonds formed?
Either giving an atom away, taking or sharing an electron. Only electrons are involved (nuclei aren’t changed). The reaction is quite hard to revert
Ionic bonding
Metal atoms lose electrons to form positive ions and non-metal atoms gain electrons to form negative ions. The opposite charges of the ions mean that they are strongly attracted to each other and cancel each other out (neutral)
Molecule
Compounds formed from non-metals
Covalent bonding
Each atom shares an electron with another atom
Properties of compounds vs their original elements
Very different chemically and physically
Format of symbol equation
x y z
x + y -> z
What do chemical changes show
The atoms on both sides but they have to be equal because of the law of conservation of mass
Mixtures
Lots of separate things but aren’t chemically bonded together with a chemical bond. They can consist of elements or compounds
Is air a mixture?
Yes
Do the properties of mixtures change?
No because they aren’t chemically changed
Examples of mixture separation techniques
Chromatography, filtration, evaporation, crystallisation, (fractional) distillation
Chromatography
Paper chromatography is used to separate mixtures of soluble substances. These are often coloured substances such as food colourings, inks, dyes or plant pigments.
Chromatogram
The end result of the pattern created by chromatography
When can filtration be used?
Of your product is an insoluble solid that needs to be separated from a liquid reaction mixture. It can also be used in purification as well
Insoluble meaning
Cannot be dissolved into the liquid
Evaporation separation technique
If a solid can be dissolved it’s soluble, so you can slowly heat the solution and the solvent will evaporate from the solution. Thus the solution will become more concentrated and crystals will start to form. What is left are dry crystals
Crystallisation separation technique
Gently heat the solution and some of the solvent will evaporate and gets more concentrated. Once some of the solvent has evaporated, remove the dish and let it cool and the salts should start to form crystals as it becomes insoluble in the cold
What can filtration and crystallisation be used for?
To separate rock salt
What is distillation used for?
Separating a liquid from a solution
How to distil a solution
Heat the solution and the part of the solution that has the lowest boiling point evaporates first, which is then cooled, condensed and collected. The rest of the solution is left behind in the flask.
Fractional distillation
Used to separate a mixture of liquids
How to fractionally distil a mixture of liquids
Put mixture in flask and stick a fractionating column. Different liquids will have different boiling points, so they will evaporate at different rates.
First theory of the Atom (John Dalton)
Described atoms as solid spheres and said that different spheres made up the different elements (Plum Pudding Model)
J J Thomson (Atom)
in 1897, he concluded that atoms weren’t solid spheres and measure the charge and mass which showed that an atom must contain even smaller negatively charged particles (electrons)
What did the Plum Pudding model show?
An atom as a ball of positive charge with electrons stuck in it
Ernest Rutherford (Atom)
Famous alpha particle scattering experiments. They fired positively charged alpha particles at an extremely thin sheet of gold. From the plum pudding model, they expected the particles to pass straight through or be slightly deflected. Most did go through but some deflected more than expecte.d, and some even backwards. This disproved the plum pudding model
Rutherford’s Nuclear model
Tiny positively charged nucleus at the centre, where most of the mass is concentrated. A ‘cloud’ of electrons surround the nucleus, which meant most of the atom was empty space
Bohr’s Nuclear Model
Bohr proposed that electrons orbit the nucleus in fixed shells and aren’t anywhere in between which is a fixed distance from the nucleus. Rutherford’s model was most wrong because then the atom would collapse.
Proof of existence of protons
Rutherford and others showed that the nucleus can be divided into smaller particles, which have the same charge as the hydrogen nucleus
Proof of existence of neutrons
20 years after the idea of nuclei, James Chadwick carried out an experiment which provided evidence for neutral particles in the nucleus
Electron shell rules
- Electrons always occupy shells
- Lowest energy levels are always first
- Only a certain number of electrons are allowed in each shell (1: 2, 2: 8, 3: 8)
- Atoms are more stable when they have full electron shells
- Most atoms want to react because it’s outer shell is not full
Electronic structure
How many electrons in each shell, e.g. Calcium
2, 8, 8, 2; proton number = 20
In the 1800s, how was the periodic table sorted?
They were sorted from these:
- Physical and chemical properties
- Atomic weight
Because of this, they were sorted in the order of atomic weight and a periodic pattern was noticed in the properties of the elements. Early periodic tables were not complete and some elements were placed in the wrong group. This happened because they were placed in the order of atomic weight and did not take into account their properties.
Dmitri Mendeleev
In 1869, he put 50 known elements and arranged them into his Table of Elements. He mainly put them in order of atomic weight, but did switch that order if the properties meant it should be changed. Gaps were left in the table made sure that elements with similar properties stayed in the same groups. When they found them, it fitted the pattern and confirmed Mendeleev’s ideas.
How many elements are there
Over 100 elements
How are elements arranged in the periodic table
In the order of increasing atomic number
Columns
Elements with similar properties (horizontal)
Groups
Vertical columns
What does the group number tell you?
How many electrons there are in the outer shell
What are the rows called?
Periods
Metal Fact
Most elements are metals
What are metals?
Elements which can form positive ions when they react.
Non metals
Don’t generally form positive ions
How an atom’s electronic structure affect how they will react?
Metals towards the left are more reactive but they have less electrons to lose. For non-metals, forming positive ions is much more difficult as they are either to the right of the periodic table. Instead they need to gain an electron
Metal Properties
Metallic bonding which causes them to have similar physical properties.
- Strong (hard to break)
- Can be bent or hammered
- Great at conducting heat and electricity
- High boiling and melting points
Non-metal properties
Don’t have metallic bonding
- More brittle
- Dull looking
- Generally can’t conduct electricity
- Lower density
Group 1 metals
Alkalis (lithium, sodium, potassium, rubidium, caesium and francium)
Group 1 metal similarities
Very reactive, soft, low density, 1 electron in their outer shell
Properties as you go down Group 1
- Increasing reactivity
- Lower melting and boiling points
- Higher relative atomic mass
What do Alkali metals form when they react with Non-Metals?
Ionic compounds
Ionic compound properties
Generally white solids that dissolve in water to form colourless solutions
What happens when you react Water with Alkalis?
- Produce hydrogen gas
- React very vigorously
- As you go down the group the more violent the reaction
- Lithium, sodium and potassium float and move around the surface, fizzing furiously
- Potassium and below is enough to ignite the hydrogen
- Form hydroxides that dissolve in water to give alkaline solutions
Alkali Reactions with Chlorine
Produces a salt to form white salts called metal chlorides
Alkalis react with Oxygen
Form a metal oxide
Group 7 elements
Halogens
- All non metals with coloured vapours
Flourine
Very reactive, poisonous yellow gas
Chlorine
Fairly reactive, poisonous dense green gas
Bromine
Dense, poisonous red brown volatile liquid
Iodine
Dark grey crystalline solid (purple vapour)
How do halogens exist
As molecules which are pairs of atoms
As you go down group 7 …
They become less reactive, have higher melting and boiling points, have higher relative atomic masses
What can halogens form?
Molecular compounds
What do halogens and metals form?
Ionic bonds. Halogens form with 1- ions called halides. The compounds that form have ionic structures.
What happens when more reactive halogens react with less reactive ones?
Higher reactive halogens will displace less reactive ones
Group 0 elements
Noble gases
Noble gasses properties
- Full set (8) of outer electrons apart form Helium (2). As they are stable, they don’t give up or gain electrons to become more stable (Inert).
- Exist as monatomic gases (single atoms not bonded to each other)
- All elements in group 0 are colourless gases at room temperature
- Non flammable
As you go down the noble gasses…
Boiling points increase
Why do boiling points increase the further down you go noble gasses?
They have more electrons which lead to a greater intermolecular force between them which need to be overcome.
