Atomic Structure and the Periodic Table Flashcards
What are atoms?
- smallest part of an element
- radius of about 0.1 nanometers (1 times 10 to the power of -10)
What are the relative masses and charges of the three particles in atoms?
Proton- relative mass of 1 and charge of +1
Neutron- relative mass of 1 and charge of 0
Electron- relative mass of very small (0 basically) and a charge of -1
What is the overall charge of an atom and why?
- Atoms are neutral (they have no overall charge)
- This is because they have the same number of protons and electrons
- Protons and electrons have opposite charges of the same size so they cancel each other out
What is the difference between an ion and an atom?
- In an ion the number of protons doesn’t equal the number of electrons
- An ion has an overall charge due to lost or gained electrons
What is an atomic number?
the number of protons in the atom
What is a mass number?
the total number of protons and neutrons that there are in an atom
What is an element?
A substance made up of only one type of atom (fixed number of protons in each atom)
What are isotopes?
- Isotopes are different forms of the same element
- They have the same number of protons but a different number of neutrons
- This means they have the same atomic number but a different mass number
What is the formula for working out the relative atomic mass of an element?
relative atomic mass=
sum of abundances of all the isotopes
What are compounds?
-Compounds are substances formed from two or more elements chemically combined in fixed proportions and positions
How do you separate the elements out of compounds?
Through chemical reactions
Do compounds have similar properties to the elements they are made of?
-No, they are usually totally different
How do we show what atoms are in a compound?
-We use formulas that are made up of elemental symbols in the same proportions that the elements can be found in the compound
What is the formula for Ammonia?
NH3
What is the formula for Sodium Chloride?
NaCl
What is the formula for Hydrochloric acid?
HCl
What is the formula for Calcium Chloride?
CaCL2
What is the formula for Sodium Carbonate?
Na2CO3
What is the formula for Sulfuric Acid?
H2SO4
What are reactants?
-Reactants are the molecules and ions and elements on the left hand side of the arrow in a chemical reaction equation because they react with each other
What are products?
-Products are the molucules and ions on the right hand side of the arrow in a chemical reaction equation because they have been produced from the reactants
What are mixtures?
two or more elements or compounds not chemically combined
Name the physical methods for separating parts of a mixture out:
- Filtration
- Crystallisation
- Simple Distillation
- Fractional distillation
- Chromatography
What are the properties of a mixture?
The properties of a mixture are just the properties of the separate parts. The chemical properties of a substance aren’t affected by it being a mixture
When can filtration be used?
If an insoluble product needs to be separated from a liquid reaction mixture. It can also be used in purification
How is filtration carried out?
The mixture is placed in cone shape filter paper which is in a funnel and a beaker. The liquid molecules are small enough to pass through the filter paper but the solid product does not and thus, separating them.
What is a solid that can be dissolved?
A solute
How are soluble salts separated from a solution?
Using crystallisation or evaporation
What is distillation?
A process used to separate mixtures which contain liquids.
What is the simple distillation process?
1) Solution is heated. Part of the solution which has the lowest boiling point evaporates first.
2) The vapour is cooled by cold water flowing around the tube (condenser) in which the vapour is travelling through from where it evaporated
3) The vapour condenses and is collected
4) The rest of the solution is left behind in the flask
What is the disadvantage of the simple distillation process?
It can only be used to separate things with very different boiling points
What is the fractional distillation process?
1) The mixture is put in a flask and a fractionating column is put on top. It is then heated.
2) The different liquids evaporate at different temperatures
3) The liquid with the lowest boiling point evaporates first and when the temperature on the thermometer matches the boiling point of this liquid it will reach the top of the column.
4) It will then go through a condenser and be collected
5) The liquids with higher boiling points will only get part the way up the column before condensing and running back down towards the flask
6) Once the first liquid has been collected, the temperature is raised until the next liquid reaches the top of the column and so on
What did JJ Thomson in 1897 discover about atoms?
He discovered that atoms were not a solid sphere. After measuring the charge and mass of an atom, he found that an atom must contain even smaller, negatively charged particles called electrons.
What theory did JJ Thomson devise?
the plum pudding model
Who proved that the ‘plum pudding model’ was wrong and how?
Ernest Rutherford and his student Ernest Marsden using the famous alpha particle scattering experiment
What is the alpha particle scattering experiment?
It is the firing of positively charged alpha particles at an extremely thin sheet of gold.
What did the Ernests expect to happen in the Gold Leaf Experiment?
They expected the particles to pass straight through the sheet or be slightly deflected at most. This was because the ‘plum pudding’ theory led them to believe that the positive charge of each atom was spread out throughout the ‘pudding’ of the atom.
What actually happened in the Gold Leaf Experiment?
Most the particles did go through the gold sheet but some were deflected more than expected. A small number were also deflected backwards. The plum pudding model couldn’t be right
What theory did Rutherford come up with to explain this new evidence?
He came up with the nuclear model of an atom
What is Ernest’s nuclear model of an atom?
In the model, there is a tiny positively charged nucleus at the centre, where most the mass is concentrated. A ‘cloud’ of negative electrons surround the nucleus so most the atom is empty space.
How did Rutherford’s model explain what had happened in the experiment?
It showed that when the alpha particles came near the concentrated, positive charge of the nucleus, they were deflected. If they were fired directly at the nucleus, they deflected backwards, otherwise they just passed through the empty space.
What was the flaw in Rutherford’s model?
Scientists realised that the electrons in a ‘cloud’ around the nucleus of an atom, would be attracted to the nucleus, causing the atom to collapse.
Who developed Rutherford’s theory to fix the flaw in it?
Niles Bohr
How did Niles Bohr develop the model of the atom?
In his model, the atom suggested that the electrons were contained in shells. He proposed that the electrons orbit the nucleus in fixed shells and aren’t anywhere between. Each shell was a fixed distance from the nucleus.
Was Niles Bohr’s theory supported?
Bohr’s theory was supported by many experiments and it also helped explain the observations that scientists were seeing at the time
How was the existence of the proton discovered?
The likes of Ernest Rutherford and others, found through experiments that the nucleus can be divided into smaller particles, which each have the same charge as a hydrogen nucleus. These particles were named protons.
How was the existence of the neutron discovered?
About 20 years after scientists accepted that atoms have nuclei, James Chadwick carried out an experiment which provided evidence for neutral particles in the nucleus which are now called neutrons.
How were elements arranged in the early 1800s?
They were arranged in order of relative atomic mass. A periodic pattern was noticed in the properties of the elements. Hence why it was called the periodic table (Newland’s Theory of Octaves)
How did Dmitri Mendeleev overcome some of the problems in the first periodic table in 1869?
- He took the 50 known elements and put them into his Table of the Elements in order of atomic weight
- left gaps for predicted elements
- some of the elements weret were switched if they had a similar property to another element (like iodine and tellurium as iodine was similar to chlorine and bromine)
Why were gaps left in Mendeleev’s table?
Some of the gaps indicated the existence of undiscovered elements and allowed Dmitri to predict what those properties. The gaps were also made to make sure that the elements with similar properties stayed in the same groups.
What does the group number tell you?
The group number tells you how many electrons are in the outer shell
What are the rows called and what do they symbolise?
The rows are called periods and each period number represents the number of shells of electrons.
What do atoms usually react to gain?
A full outer shell made via gaining, losing or sharing electrons
Why are metals at the bottom of the groups easier at losing electrons?
- Metals to the bottom have outer shell electrons that are a long way from the nucleus, so fell a weaker attraction.
- Less energy is needed to remove the electrons at the bottom
- Electron shielding makes it easier to lose the electron too
What are the similar properties of all metals due to metallic bonding?
- Strong and malleable
- Good at conducting heat and electricity
- Have high boiling and melting temperatures
What are transition metals?
- unreactive in air and water
- high melting and boiling points
- Dense, strong, shiny
- form more than one type of ion
- form coloured compounds
- Often good catalysts
What are the properties of the group 1 elements?
- soft
- low density
- very reactive in air and water
- only form +1 ions
- only react to form white compounds
What is the trends for the alkali metals as you go down group 1? Why?
- Increasing reactivity
- atomic radius increases
- meaning the outer shell electron is further from the nuceleus
- there are also more electron shells, increasing the effects of electron shielding
- attraction of the nucleus to the outer electron is weaker so the outer electron is more easily lost so reacts faster
How does the energy output vary down the group when alkali metals are reacted with water?
The amount of energy as you go down the group increases ie. potassium releases enough energy to ignite hydrogen
What is the trend down group 7?
decreasing reactivity
What do the more reactive halogens do to the less reactive ones when in an aqueous solution of its salt?
They will displace the less reactive ones e.g chlorine gas displaces iodine from potassium iodide
What are the properties of noble gases ?
- They all have eight electrons in their outer energy level apart from helium which has two, giving most of them a full outer-shell.
- They don’t react/inert because their outer shell is energetically stable
- Monatomic gases
- Colourless gases at room temperature
- Non flammable
- low boiling/melting points which increasing down the group
Why was Newland’s Theory of Octaves Rejected by some scientists?
- His theory only worked for the first 20 elements known at the time
- New elements had nowhere to go
- Copper was in the same group as Li, Na and K which react with water but copper does not react with water
Define soluble
A property where the substance can dissolve in a certain solution
Define insoluble
A property where the substance cannot dissolve in a solution
Define a solute
A solute is a substance(solid) which is dissolved
Define solvent
The liquid that dissolves the solute
Define solution
A combination of a solute dissolves in a solvent
What is the relative molecular formula mass?
The sum of all the individual atomic masses for atoms present in the formula of the molecule
How do we see if carbon dioxide is present?
The gas will bubble through limewater and make it go cloudy
How do we see if hydrogen is present?
A lit splint will make a squeaky pop
How do we see if oxygen is present?
A glowing splint will be relighted
Why did some scientists suggest that Mendeleev’s table was incorrect?
- Some chemists thought all elements had been discovered so there was no need for gaps
- He put some metals in the same group a non-metals (Bromine with Manganese)
- some groups only had two elements
What is the definition of relative atomic mass?
The average mass value for an element, weighted according to the abundance of its isotopes, on a scale where Carbon-12 has a mass of 12.
What is the plum pudding model?
- single ball of positive charge with negatively charged electrons in it
- no nucleus
- mass spread throughout atom
- no empty space
- no neutrons
What are the two isotopes of Chlorine and their abundances?
Cl-35 : 75%
Cl-37 : 25%
Why are alkali metals stored in oil?
to stop them reacting with the air
What can be observed when alkali metals react with air?
- metal oxide forms a dark layer on the surface of the metal
- tarnishing
What can be observed when alkali metals react with chlorine?
- react to form a white salt (metal chloride)
How does lithium react with water?
- lots of fizz
- floats on water
- gives off gas
- dissolves and disappears
How does sodium react with water?
- floats on water
- moves around on water surface
- gives off gas
- dissolves and disappears
- more bubbles than lithium
How does potassium react with water?
- floats on water
- bursts into lilac flames
- lots of gas given off
- dissolves faster
What is the pH of the water after reacting with a group 1 metal? Why?
Alkaline pH as the metal hydroxide is produced which is an alkali
What is the explanation for the decreasing reactivity down group 7?
- atomic radius increases down the group
- meaning the outer electrons are further from the nucleus
- there are also more electron shells down the group, increasing effects of electron shielding
- meaning the attraction to the nucleus decreases so electrons are gained less easily
What are halogens?
Poisonous, coloured elements in group 7
What is fluorine? (room temp)
a yellow gas
What is chlorine? (room temp)
green gas
What is bromine? (room temp)
dark red/orange coloured liquid
What is iodine? (in all states)
Grey/black solid
brown liquid
purple gas
What is astatine? (room temp)
A black solid
What is chlorine used for?
Sterilising drinking water (kills bacteria)
What are fluoride ions used for?
Added to drinking water to prevent tooth decay
What happens when a halogen reacts with a metal?
reacts to form a white salt
What are the similar physical properties of alkali metals and transition metals?
- good conductor of heat and electricity
- malleable and ductile
- shiny
What are the different physical properties of alkali metals and transition metals?
- alkali have a low density and float on water
- alkali are soft so are easily cut
- alkali aren’t as strong
- alkali have lower melting and boiling points
Examples of transition metals used as catalysts:
- iron in the manufacture of ammonia
- nickel used to harden margarine
What chemical property of transition metals makes them good for ceramics?
They form coloured compounds which can make coloured ceramics
What are the uses of copper?
- wiring
- water pipes
Why is copper used for wiring?
- good conductor of electricity
- malleable
- ductile
Why is copper used in water pipes?
- does not react with water
- malleable
- high melting point
Why was Mendeleev’s table more accepted than Newland’s?
- Left gaps for undiscovered elements but Newland didn’t
- Changed the order of some elements like Tellerium and Iodine to fit properties of groups whereas Newland didn’t and his groups were less accurate
- Mendeleev predicted the properties of missing elements
- these elements were discovered and his predictions were correct and the elements fitted in the gaps
What were the similarities between Mendeleev’s and Newland’s tables?
- both missed noble gases
- both had more than one element in a box
- chemically similar elements in same column
- arranged elements in order of atomic weight
