Atomic structure & periodic table Flashcards
What defines an element?
all the atoms are the same
where are elements displayed?
in the periodic table
what is a compound?
Two or more different elements chemically combined in fixed proportions
what are properties of compounds like?
Compounds usually have totally different properties to the elements that they’re made from
Mixture
Different elements or compounds that are not chemically combined
give an example of a physical separation method:
- Filtration
- Distillation
- Crystallization
- Chromatography
What is a molecule?
Any elements chemically combined, even if they’re the same element
give an example of a molecule:
- Methane
- Water
- Ammonia
Describe a proton:
it is found in the nucleus of an atom, has a relative mass of 1, and a charge of +1
Describe a neutron:
it is found in the nucleus of an atom, has a relative mass of 1, and a charge of 0
Describe an electron:
they move around the nucleus in shells, cover a large amount of space, they have a very small relative mass and a charge of -1
What does the atomic number tell you?
How many protons there are
What does the mass number tell you?
the total number of protons and neutrons in the atom
How do you find the number of electrons?
subtract the atomic number from the mass number
What is an isotope?
Atoms of the same element with different numbers of neutrons
What is the nucleus?
Region of the atom that contains protons and neutrons
what are ions?
Atoms that gain or lose electrons to form ions with opposite charge
what is separation by distillation?
Components with higher boiling points remain in the retort, while components with lower boiling points are collected in the collector
what do chemical equations show?
chemical changes
What do you have to do if you have a symbol equation?
Keep it balanced
What is a mixture?
lots of elements and compounds mixed together, but not chemically bonded
Describe separating a mixture through evapouration:
1) slowly heat the solution in an evaporating dish
2) the solvent will evaporate and the solution will get more concentrated. Eventually, crystals will start to form
3) Keep heating the evaporating dish until all you have left are dry crystals
Describe separating a mixture through filtration:
1) add the mixture to filter paper that is in a cone shape
2) place this into a beaker, and let the mixture separate
Describe separating a mixture through crystallisation:
1) add the solution to an evaporating dish and gently heat the solution. Some will evaporate and the solution will get more concentrated
2) once some of the solvent has evaporated, or when you see crystals forming, remove the dish and allow to cool.
3) the salt should start to form crystals as it becomes insoluble in the cold, high concentrated solution
4) Filter the crystals out of the solution, and leave in a warm place to dry - can use a drying oven or desiccator
Describe simple distillation:
1) it is used to separate out a liquid from the solution
2) heat the solution, so that the part of the mixture with the lowest boiling points starts to evaporate
3) The vapour is then cooled, condensed and collected
4) the rest of the solution is left behind in the beaker
Describe fractional distillation:
1) this is used to separate a mixture with several different elements/compounds
2) You heat the solution so that the different elements evaporate at different boiling points
3) the different components will cool at different points of the fractionating column, so they then condense and are collected at different points.
4) this is useful for separating things like crude oil
What is the order of the atomic structure over time?
start of 19th century - atoms are solid spheres
1897 - plum pudding model
1909 - nuclear model
1912 - electrons are in shells
1932 - atomic model (neutrons)
Describe the development of the idea that atoms are solid spheres:
At the start of the 19th century, John Dalton described atoms as solid spheres, and said that different spheres made up different elements.
Describe the development of the plum pudding model:
in 1897 JJ Thomson concluded that atoms were not solid spheres. His measurements of charge and mass showed an atom must contain even smaller, negatively charged particles (electrons) The plum pudding model embedded in it.
Describe the development of the nuclear model:
In 1909, Ernest Rutherford and his student Ernest Marsden conducted the famous alpha scattering experiments. They fired positively charged alpha particles at a thin sheet of gold. From the plum pudding model, they were expecting the particles to pass through the sheet (or be deflected slightly). After doing the experiment, they saw lots get deflected more than expected. This suggested that there was a tiny, positive nucleus at the centre, and a cloud of electrons surrounded this, the atom is mostly empty space.
Describe the development of electrons in shells in the atomic model:
At the beginning of the 20th century, scientists realised that electrons in a “cloud” around the nucleus of an atom would be attracted to the nucleus causing the atom to collapse. Niels Bohr’s nuclear model shows the electrons were contained in shells that are in fixed shells, orbiting the nucleus.
Describe the development of the existence of protons and neutrons.
- Rutherford discovered that the nucleus can be divided into smaller particles, which each have the same charge as a hydrogen nucleus. These particles were named protons.
- around 20 years later James Chadwick carried out an experiment which gave evidence for neutral particles in the nucleus - neutrons. This discovery resulted in a model of the atom which was pretty close to the one now - the nuclear model
What are the electron shell rules?
1) electrons always occupy shells - also known as energy levels
2) the lowest energy levels are always filled first - these are closest to the nucleus
3) only a certain number of electrons are allowed in each shell - all shells have 8 excluding the first shell, this has 2
4) atoms prefer to have full electron shells
5) in most atoms the outer shell is not full, which is why the atoms reacts to fill the outer shell.
what does the number of protons determine?
The number of protons determines the element’s identity (atomic number).
what charge does an electron and proton have?
Electrons have a negative charge (-1), while protons have a positive charge (+1).
How was the periodic table organised in the 1800s?
1) arranged by their physical and chemical properties
2) their relative atomic mass
What did Dmitri Mendeleev do?
1) In 1869, Mendeleev overcame some of the issues with the periodic table by taking 50 known elements and arranging them into his Table of Elements - leaving gaps throughout
2) Mendeleev put the elements mainly in order of atomic mass, but did switch that order to make sure the similar elements are grouped together
3) Gaps were left because Mendeleev believed that some elements had not been discovered yet due to the patterns in the periodic table.
Most elements are metals - describe them:
1) metals are elements which can form positive ions when they react
2) they are towards the bottom and to the left of the periodic table
3) most elements are metals
4) non metals are at the far right and top of the periodic table
5) non metals do not usually form positive ions when they react
What properties do metals have?
- they are strong (hard to break), but are malleable (can be bent or hammered into shapes)
- they are good conductors of heat and electricity
- they have high boiling and melting points
what properties do non-metals have?
1) dull looking
2) more brittle
3) are not always aren’t always solids at room temperature
4) do not generally conduct electricity and often have a lower density
What are the transition metals and where are they found?
1) they are between group 2 and group 3 in the periodic table
2) transition metals are typical metals, and have properties you would expect of a “proper” metal - they are good conductors of heat and electricity.
3) they are very strong, dense and shiny
4) transition metals can have more than one ion
5) transition metals are often coloured
6) transition metals are often used as good catalysts
describe the group 1 elements:
- the alkali metals are in group 1
- they have one electron in the outer shell, so they are very reactive
- the alkali metals are soft and have low density
- as you move down the group; the reactivity increases, lower melting/boiling points, higher relative atomic mass
How do the alkali metals react with oxygen, chlorine and water?
oxygen - react to form a metal oxide, forms a dull metal oxide layer
chlorine - react vigorously when heated in chlorine gas, forms metal chloride salts
water - reacts vigorously when put in water, produces hydrogen gas and metal hydroxides
describe the group 7 elements:
- the halogens are all non-metals with coloured vapours
- all exist as molecules which are pairs of atoms
- as you go down the group; becomes less reactive, higher melting and boiling points, higher relative atomic mass
describe each of the individual group 7 elements:
- fluorine is very reactive, yellow gas
- chlorine is fairly reactive, green gas
- bromine is a dense, red-brown volatile liquid
- iodine is a dark grey solid or purple vapour
what type of bonds do halogens form?
they form ionic bonds with metals
what are the group 0 elements?
- they are all inert, colourless gases
- they all have 8 electrons in the outer shell, apart from helium which has two {they all have full outer shells}
- they exist as monatomic gases - single atoms not bonded to each other
- since they are inert, they are non-flammable
- as you move down the group; the boiling points increase, relative atomic mass increases
why do the group 0 boiling points increase as you move down the group?
It is due to an increase in the number of electrons in each atom leading to greater intermolecular forces between them which need to be overcome.
