Atomic Structure and the Periodic Table Flashcards
What are atoms?
- Atoms make up all substances
- The smallest part of an element
- They contain Protons, Neutrons and Electrons
- They have a radius of about 0.1 nanometers (1 times 10 to the power of -10)
What is the nucleus like in an atom?
- The nucleus is in the middle of the atom
- The nucleus contains protons and neutrons
- This means the nucleus has a positive charge because of the protons
- The whole mass of the atom is concentrated in the nucleus
- It has a radius of around 1 x 10 to the power of -14m which is around 1/10000 of the radius of the atom
What are the electrons in an atom?
- Electrons move around the nucleus in electron shells
- They are negatively charged and tiny but can cover a lot of space
- The volume of their orbits determines the size of the atom
- They have virtually no mass (negligible 1/1840)
What are protons, neutrons and electrons all called?
Particles
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 (+ve) or gained (-ve) electrons
- when atoms react they lose, gain or share electrons
- e.g. Ca2+ (lost 2 electrons)
- e.g. N3- (gained 3 electrons)
What is an atomic number?
- An atomic (proton) number tells you how many protons there are in an atom
- e.g. for Ca2+ atomic number is 20 (20 protons), therefore 18 electrons
- e.g. for N3- atomic number is 7 (7 protons), therefore 10 electrons
What is a relative atomic mass (RAM) number?
- A mass number tells you the total number of protons and neutrons that there are in an atom
What is an element?
- A substance made from only 1 type of atom - they have a fixed number of protons (same atomic number)
How are the types of atoms decided?
- Atoms can have different numbers of electrons, protons and neutrons.
- The number of protons in the nucleus decides what type of atom it is
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
How is the issue fixed in naming elements as they can be in the form of different isotopes?
Relative atomic mass is used when referring to an element as a whole
What does “Carbon-12” mean for example?
- This means there are 6 protons in this isotope as it is Carbon which is an element
- It also means there are 6 neutrons because the 12 is the mass number (12-6=6)
What is the formula for working out the relative atomic mass of an element?
relative atomic mass (RAM)
= sum of (isotope abundance x isotope mass number)
sum of abundances of all the isotopes
What are compounds?
- Compounds are substances formed from two or more elements
- The atoms are in fixed proportions throughout the compound and are held together by chemical bonds
How are the chemical bonds made?
- Making bonds involves atoms giving away, taking or sharing electrons.
- The Nuclei aren’t affected
How do you separate the elements out of compounds?
Through chemical reactions
What do compounds formed of a metal and non-metal element consist of?
- The compound consists of ions
- The metal atoms lose electrons to form positive ions
- The non-metal atoms gain electrons to form negative ions
What do the positive and negative ions in a compound consisting of a metal and non-metal element do?
They undergo ionic bonding due to the strong electrostatic attraction between the two polar charged ions
What do compounds formed of non-metals consist of?
- These compounds consist of molecules
- Each atom shares an electron with another atom, this is called covalent bonding
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 a reaction between 1 carbon atom and two oxygen atoms?
CO2 (Carbon dioxide)
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
How can you show a chemical reaction?
- With a word equation
- With a symbol equation
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?
- Mixtures are formed of compounds and elements that have no chemical bond between them e.g. flour and sugar (before baking!)
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
What is paper chromatography?
A technique that can be used to separate different dyes in an ink
What is the set up for the paper chromatography process?
1) Draw a straight line near the bottom of filter paper using a pencil (pencil marks are insoluble)
2) Add a spot of ink to the line and place the paper in a solvent e.g. water or ethanol (some compounds dissolve well in water but others don’t)
3) Make sure the ink isn’t touching the solvent
4) Place a lid on the solvent container to stop the solvent evaporating
What should happen after setting up the chromatography process?
- The solvent will seep up the paper, carrying the ink with it
- Each different dye/pigment in the ink will move up the paper at different rates so the dyes will separate out and form a spot in a different place
- The insoluble inks in the dye will stay on the baseline
- The end result is a pattern of spots called a chromatogram
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 proprty does a solid have if it can be dissolved?
soluble
How are soluble salts separated from a solution?
Using evaporation or crystallisation
How is evaporation carried out?
1) The solution is poured into an evaporating dish
2) The solution is slowly heated. The solvent will evaporate and the solution will get more concentrated. Eventually, crystals will start to form 3) The dish is heated until dry crystals are left
What is an advantage and disadvantage of using evaporation to separate parts of a soluble salt?
The method is quick but can only be used if the salt does not decompose when it is heated unlike in crystallisation.
How is crystallisation carried out?
1) The solution is gently heated in an evaporating dish.
2) Once some of the solvent has evaporated or when crystals start to form, remove the dish from the heat and leave to cool
3) The salt should start to form crystals as it becomes insoluble in the cold, highly concentrated solution
4) Filter the crystals out of the solution and leave them in a drying oven or desiccator to dry
What is distillation?
- A process used to separate mixtures which contain liquids.
- The main two types of distillation are fractional and simple.
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 were atoms described as at the start of the 19th century?
John Dalton concluded atoms were solid spheres and different spheres made up the different elements
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.