Atomic structure and the periodic table Flashcards
What is an atom?
An atom is the smallest part of an element that can exist.
What is an element?
An element is a substance of only one type of atom.
How are the elements listed and approximately how many are there?
There are listed in the periodic table and there are approximately 100.
Elements can be classified into 2 group bases on their properties, what are they?
Metals and non-metals.
Elements may combines through chemical reactions to form new products; what are they new substances called?
Compounds.
What is a compound?
2 or more elements combined chemically in fixed proportions which can be represented by formula.
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 2 more more elements or compounds not chemically combined together; it does have the same chemical properties.
What the methods through which mixtures can be separated (there are five)? Do these involve chemical reactions?
- Filtration.
- Crystallisation.
- Simple distillation.
- Fractional distillation.
- 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 an 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 a separation of a solid dissolved in a solvent from a solution such as salt from H₂O. The solution is heated until all the solvent evaporates; the solid 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 different boiling points.
The apparatus is similar to the one of simple distillation apparatus, with the additional fractional column placed on top of the heated flask.
The fractional column contains glass beads. It helps to separate compounds. In industry, mixtures are repeatedly condensed and vaporised. The column is hot at the bottom and cold at the top. The liquid will condense at different heights of the column.
Describe and explain filtration
Filtration is used to separate an insoluble solid 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 2 distinct layers in the separatory 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 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.
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 = very small/0, 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.
What is the radius of a nucleus and what is it compared to that of the atom?
1 x 10⁻¹⁴.
1/10,000.
What name is given to the number of protons in the nucleus?
Atomic number.
Atoms of the same element have the same number of which particle in the nucleus?
Protons.
Where is the majority of mass of an atom?
The nucleus.