GCSE AQA Chemistry - Topic 1 - ATOMIC STRUCTURE AND THE PERIODIC TABLE Flashcards
What is an atom?
the smallest part of an element that can exist
What is an element?
a substance of only one type of atom
How are the elements listed and approximately how many are there?
they are listed in the periodic table; there are approximately 100
Elements can be classified into two groups based on their properties; What are these groups?
metals and non-metals
Elements may combine through chemical reactions to form new products; What are these new substances called?
compounds
What is a compound?
two or more elements combined chemically in fixed proportions which can be represented by formulae
Do compounds have the same properties as their constituent elements?
no, they have different properties
What is a mixture? Does it have the same chemical properties as its constituent materials?
a mixture of two or more elements or compounds not chemically combined together; it does have the same chemical properties
What are the methods through which mixtures can be separated? [5] Do these involve chemical reactions?
Filtration, crystallisation, simple distillation, fractional distillation, and chromatography; they do not involve chemical reactions.
Describe and explain simple distillation.
simple distillation is used to separate liquid from a solution - the liquid boils off and condenses in the condenser. the thermometer will read the boiling point of the pure liquid. contrary to evaporation, we get to keep the liquid.
Describe and explain crystallisation/evaporation.
Evaporation is a technique for separation of a solid dissolved in a solvent from a
solvent (e.g. salt from H2O).
The solution is heated until all the solvent evaporates; the solids stays in the vessel.
Crystallisation is similar, but we only remove some of the solvent by evaporation to
form a saturated solution (the one where no more solid can be dissolved). Then,
we cool down the solution. As we do it, the solid starts to crystallise, as it becomes
less soluble at lower temperatures. The crystals can be collected and separated
from the solvent via filtration.
Describe and explain fractional distillation.
Fractional distillation is a technique for separation of a mixture of liquids.
It works when liquids have different boiling points.
The apparatus is similar to the one of simple distillation apparatus, with the
additional fractionating column placed on top of the heated flask.
The fractionating column contains glass beads. It helps to separate the compounds.
In industry, mixtures are repeatedly condensed and vapourised. The column is hot at
the bottom and cold at the top. The liquids will condense at different heights of the
column.
Describe and explain filtration
Filtration is used to separate an insoluble solid is suspended in a liquid. The insoluble solid (called a residue) gets caught in the filter paper, because the particles are too big to fit through the holes in the paper. The filtrate is the substance that comes through the filter paper. Apparatus: filter paper + funnel.
Describe and explain chromatography.
Chromatography is used to separate a mixture of substances dissolved in a solvent.
In paper chromatography, we place a piece of paper with a spot containing a mixture
in a beaker with some solvent. The bottom of the paper has to be in contact with
the solvent. The solvent level will slowly start to rise, thus separating the spot
(mixture) into few spots (components).
What is a separating funnel?
A separating funnel is an apparatus for separating immiscible liquids. Two immiscible liquids of different densities will form two distinct layers in the separating funnel. We can run off the bottom layer (the liquid with greater density) to a separate vessel.
Describe the plum-pudding model
The atom is a ball of positive charge with negative electrons embedded in it.
Describe the Bohr/Nuclear model and how it came about
The nuclear model suggests that electrons orbit the nucleus at specific distances (shells) - it came about from the alpha scattering experiments
Later experiments led to the discovery of smaller, positive particles in the nucleus; What are these particles called?
Protons
What did the work of James Chadwick provide evidence for?
The existence of neutrons in the nucleus
Describe the structure of an atom
The atom has a small central nucleus (made up of protons and neutrons) around which there are electrons.
State the relative masses and relative charges of the proton, neutron, and electron.
Proton: mass - 1, charge - 1
Neutron: mass - 1, charge - 0
Electron: mass - v. small, charge - -1
Explain why atoms are electrically neutral
They have the same number of electrons and protons
What is the radius of an atom?
0.1 nm
