Atomic structure and the periodic table Flashcards
Atoms, elements and compounds
What is an atom?
The smallest part of an element that can exist
Atoms, elements and compounds
What is an element?
A substance of only one type of atom
Atoms, elements and compounds
What is a compound?
Two or more elements combined chemically in fixed proportions which can be represented by formulae
Mixtures
What is a mixture?
Two or more elements or compounds not chemically bonded combined together
Mixtures
Name the ways through which mixtures can be seperated.
- Filtration
- Crystallisation
- Simple and fractional distilliation
- Chromatography
Mixtures
Explain simple distilliation
Simple distilliation 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 the evaporation, we get to keep the liquid.
Mixtures
Explain crystallisation
Evaporation separates a solid dissolved in a solvent from a solvent. The solution is heated until all the solvent is evaporated.
Crystallisations is similar, but we only remove some of the solvent by evaporation to form a saturated solution. Then we cool it down. As we do it, the solid begins to crystallise, as it becomes less soluble at lower temperatures
Mixtures
Explain factional 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 addition fractionating column placed on top of the heated flask.This fractionating column contains glass beads. It helps to separate the compounds, In industry, mixtures are repeatedly condensed and vapourised. The colomn is hot at the bottom and cold at the top. The liquids will condense at different heights of the column
Mixtures
Describe 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, becuase the particles are too big to fit through the holes in the paper. The filtrate in the substance that comes through the filter paper. Apparatus: filter paper + funnel
Mixtures
Describe chromotography
Chromotography is used to separate a mixture of substances dissolved in a solvent.
In paper chromotography, 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)
The development of the model of the atom
Describe John Dalton’s (billard ball) model
A tiny sphere that is indivisable ; the first ever model of the atom
The development of the model of the atom
Describe JJ Thomsons ‘Plum pudding model’
A small ball of positive charge with negative electrons embedded throughout
The development of the model of the atom
Describe Ernest Ruthfords model
A positive nucleus surrounded by negative electrons orbitting on energy shells
The development of the model of the atom
Describe Rutherford’s alpha scattering experiment and it’s results
Rutherford directed a beam of alpha particles at a very thin gold leaf in a vacuum.
It was thought that all the particles would pass straight through. However, the results were:
- most alpha paricles did go straight through
- a smaal number of alpha particles were deflected by large angles, yet some came straight back out
The development of the model of the atom
Describe Niels Bohr’s model
Bohr adapted the nuclear model by suggesting that the electrons orbit at specific distances
The development of the model of the atom
Describe the current model
James Chadwick provided evidence for the existence of neutrons inside the nucleus. The current model consists of protons and neutrons in the nucleus and electrons orbitting on energy shells at specific distances.
Relative electrical charges of subatomic particles
State the charges of the subatomic particles
- Proton - +1
- Neutron - 0
- Electron - -1
Relative electrical charges fo subatomic particles
Why do atoms have no overall charge?
Atoms have the same number of protons as electrons. The charges cancel each other out.
Size and mass of atoms
State the relative mass of atoms
- Protons - 1
- Neutrons - 1
- Electrons - 1/2000
Size and mass of atoms
What is the radius of an atom?
0.1nm
Size and mass of atoms
Whats the radius of the nucleus?
1 x 10^14
Relative atomic mass
How do we calculate the relative atomic mass?
total mass of atoms / total number of atoms
Electronic structure
Give the electronic configurations of He (2), Be (4), F (9), Na (11) and Ca (20)
2
2,2
2,7
2,8,1
2,8,8,2
Electronic structure
What are ions?
Ions are an atom that has lost or gained electrons
Metals and non-metals
Compare the properties of metals and non-metals
Metals
- high m.p and b.p
- conducts heat and electricity
- shiny
- malleable -
- very dense
- basic oxides
Non-metals
- low m.p and b.p
- cant conduct
- dull
- brittle
- not very dense
- acidic oxides
Metals and non-metals
Why can metals conduct electricity?
Metals have delocalised electrons that can move through the solution and carry a charge+
The periodic table
How are elements grouped in the periodic table?
Elements in the same group have similar properties, and have the same number of outer shell elecrons.
Elements in the same periods have the same number of shells
Development of the periodic table
How did early scientists try to classify elements?
By arranging them in order of atomic weight. Early periodic tables were often incomplete, since many elements were unknown
Development of the periodic table
How did Döbereiner arrange the elements?
Groups of 3 (triads) with similar properties
Development of the periodic table
How did Newlands arrange the elements?
Groups of 8 (law of octaves) and stated that the element 8 places in front of it had similar properties
Development of the periodic table
Who was Dmitri Mendeleev and how did he arrange the elements?
Dmitri Mendeleev was a Russian scientist, who arranged the elements in order of increasing atomic weight. He also took into account the properties of the elements and their compounds. This meant that his table:
- had gaps in it for undiscovered elements
- showed elements with similar chemical properties lined up in groups
Group 0
What are group 0 elements commonly known as?
Noble gases
Group 0
What is the trend going down group 0?
- The atoms become larger
- The intermolecular forces between the atoms become stronger
- More energy is needed to overcome these
- The boiling points increase
Group 0
Why are the noble gases unreactive?
When elements react, their atoms complete their outer sheel by losing, gaining or sharing electrons. Group 0 elements already have a full outer shell and do not need to react.
Group 1
What are group 1 elements commonly known as?
Alkali metals
Group 1
What is the trend going down group 1?
- The atoms become larger
- The outer electron becomes further away from the nucleus
- The force of attraction decreases between the outer electron and the nucleus
- The outer electron is lost more easily
So, they get more reactive
Group 7
What are group 7 elements commonly known as?
Halogens
Group 7
What is the trend going down group 7?
- The atoms become larger
- The outer shell becomes further away from the nucleus
- The force of attraction decreases
- An outer electron is gained less easily
So, they become less reactive
Transition metals vs Group 1 elements
Compare the physical properties of alkali metals and transition metals
Alkali metals
- soft
- low density
- low m.p/b.p
Transition metals
- hard and strong
- high density
- high m.p/b.p
Transition metals vs Group 1 elements
Compare the chemical properties of alkali metals and transition metals
Alkali metals
- white/colourless compounds
- reactive
- react quickly with water
- form +1 ions
- not used as catalysts
Transition metals
- coloured compounds
- not very reactive
- react slowly with water
- form ions with different charges
- used as catalysts
Typical properties of transition metals
What are the typical properties of transition metals?
- much harder and stronger
- much less reactive
- higher melting points
These are all the general properties of metals
