C1-atomic Structure Flashcards
What is an atom
An atom is the smallest part of an element that can exist
What is an element
A relatively small number of substances are made up of only one type of atom
What do symbols in the periodic table represent
Atoms
What is are compounds
They are made up of different types of atoms chemically bonded together and are called compounds
What is the law of conservation of mass
The total mass of products formed is equal to the total mass of the reactants
Are any new atoms created or destroyed in a chemical reaction
No
What is a mixture
A mixture is made up of two or more substances (elements or compounds) that are not chemically combined together
Difference between compilions and mixtures
Compounds have a fixed composition ( the ratio of elements present is always the same in any particular compound)
Chemical reactions must be used to separate the elements in a compound.
There are chemical bonds between atoms of the different elements in the compound
Mixtures have no fixed composition (the proportions vary depending on the amount of each substance mix together)
The different elements or compounds in a mixture can be separated again more easily (by physical means using the difference in properties of each substance in the mixture)
There are no chemical bonds between atoms of the different substances in a mixture.
4 physical separation methods
Filtration
Crystallisation
Distillation
Chromatography
What is the technique of filtration used for
It is used to separate substances that are insoluble in a particular solvent from those that are soluble in the solvent.
What is crystallisation
Crystallisation is used to separate a soluble solid from a liquid
How does crystallisation work?
Heat the solution in an evaporating dish on a water bath.Heating should be stopped when the solution is at the point of crystallisation. This is when small crystals appear in a drop of solution extracted from the dish with a glass rod. The rest of the water is then left to evaporate off the saturated solution at room temp to get a good sample of sodium chloride crystals. A flat bottomed-crystallisation dish or Pétri dish can be used for this final step, to give a large surface area for the water to evaporate from.
What is distillation
Crystallisation separates a soluble solid from a solvent but sometimes you need to collect the solvent itself instead of just letting it evaporate into the air.
How does distillation work
A solution is heated and boiled to evaporate the solvent. The vapour given off then enters a condenser. This is an outer glass tube with water flowing through it that acts as a cooling ‘jacket’ around the inner glass tube from the flask here the hot vapour is cooled and condensed back into a liquid for collection in a receiving vessel. Any dissolved solids will remain in the heated flask.
What is fractional distillation?
It is an effective way of separating miscible liquids, using a fractionating column. The separation is possible because of the different boiling points of the liquids in the mixture.
How does fractional distillation work
The vapours must pass over and between the glass beads in the fractionating column before they reach the condenser. the temperature in the fractionating column is highest at the bottom of the column getting lower as the vapours rise up. The substance with the higher boiling point will condense more readily on the cooler glass beads nearer the bottom of the column. And drip back down into the flask Beneath. the substance with the lower boiling point will continue rising and pass over in the condenser where it is cool enough to turn back into the liquid state and be collected.
What is chromatography?
Paper chromatography separates mixtures of substances dissolved in a solvent as they move up a piece of chromatography paper. The different substances are separated because of their different solubilisiez in the solvent used.
How does chromatography work?
A capillary tube is used to dab a spit of the solution on a pencil line near the bottom of a sheet of absorbent chromatography paper. The paper is then placed standing in a solvent at the bottom of a beaker or tank. The solvent is allowed to soak up the paper, running through the spit of the mixture. The relative solubility of the components making up the mixture in the solvent determines how far they travel up the paper. The more soluble a substance is in the solvent, the further up the paper it is carried. Different solvents can be used to maximise separation.
plum pudding model
In 1803 John Dalton presented his atomic theory based on three key ideas:
Matter is made of atoms which are tiny particles that cannot be created, destroyed or divided.
Atoms of the same element are identical and atoms of different elements are different.
Different atoms combine together to form new substances.
At the time the theory was correct but as science developed some parts of Dalton’s theory were disproved.
In 1897 physicist J.J. Thomson discovered the electron. Using a cathode-ray tube he conducted an experiment which identified the electron as a negatively charged subatomic particle, hence proving that atoms are divisible.
Based on his investigations Thomson proposed a model of the atom known as the plum pudding model which depicted negative electrons spread throughout soft globules of positively charged material.
Rutherford Scattering
In 1909 Ernest Rutherford presented his model of the atom based on the famous gold foil experiment.
Rutherford shot a beam of positively charged particles at a thin sheet of gold foil and, based on the plum pudding model, expected the particles to pass through the foil because the positive charge of the nucleus was thought to be evenly spread out.
Some particles were scattered, however, and a few were deflected directly back, which led him to postulate that most of an atom’s mass is concentrated in a region of space at the centre of the atom called the nucleus.
In Rutherford’s model the atom consists mainly of empty space with the nucleus at the centre and the electrons orbiting in paths around the nucleus.
This model was known as the nuclear model of the atom.
The Bohr Model
In 1913 Niels Bohr further developed the nuclear model by proposing that electrons orbit the nucleus in fixed shells or orbitals located at set distances from the nucleus.
Each orbital has a different energy associated with it, with the higher energy orbitals being located further away from the nucleus.
This model solved the question of why the atom doesn’t collapse inwards due to the attraction between the positive nucleus and negative electrons circling the nucleus.
Bohr’s theory and calculations were in agreement with experimental results.
Further investigation and experimentation revealed that the nucleus could be divided into smaller particles, each one having the same mass and charge. This work led to the discovery of the proton.
The Discovery of the Neutron
In 1920 Rutherford put forward the idea of the existence of large, neutral particles within the nucleus.
His idea was based on the differences between the atomic mass and the atomic number of atoms.
In 1932 James Chadwick published a paper based on an experiment carried out by Frédéric and Irène Joliot- Curie which provided evidence for the existence of these neutral particles which were called neutrons.
what are atoms made of
protons,neutrons and electrons
what is the relative charge of sub atomic particles
protons +1 ,neutrons neutral/0 and electrons -1
what is the relative mass of protons and neutrons
both are 1
what is the charge of the atom?
Atoms contain an equal number of protons and electrons therefore no overall charge
what is the atomic number?
number of protons(=number of electrons)
what is the mass number?
number of protons + neutrons
what do atoms of the same element have?
atoms of the same element have the same number of protons in their atoms
what happens when an atom gains or looses electrons?
when an atom gains electrons it becomes a negative ion and when an atom looses electrons it becomes a positive ion
what is an isotope?
isotopes are atoms of the same element with different number of neutrons. They have identical chemical properties, but their physical properties such as density can differ.
what are the electrons in an atom arranged in
energy levels/shells
what does the amount of electrons in the outermost shell determine
it determines the way in which the element will react.
