C1 and C2 Flashcards
what is an element?
a substance with only one type of atom
what is a compound?
a substance with more than one type of atom
what do all atoms contain?
-a tiny nucleus at its centre surrounded by electrons
what is a mixture?
-made up of two or more substances that are not chemically combined together
how can mixtures be separated?
- filtration
- crystallisation
- simple distillation
how was the first person to put forward ideas about atoms?
-It was not until the early 1800s when John Dalton put forward his ideas about atoms
What were Dalton’s ideas about atoms?
- Elements only contain one type of atom
- Atoms get re-arranged in chemical reactions
- Atoms are solid spheres that cannon be split into simpler particles
Who discovered the electron?
-J.J. Thompson discovered the electron at the end of the 1800s
Who discovered the plum pudding model?
-J.J. Thompson
What were Thompson’ ideas about atoms? (plum pudding model)
- Tiny negatively charged electrons must be embedded in a cloud of positive charge
- He imagined the electrons as bits of plum in a plum pudding
What was Rutherford’s ideas about the atom?
- The positive charge of an atom must be concentrated at a tiny spot in the centre of the atom (nucleus)
- Electrons must be orbiting around the nucleus which contains very dense positively charged protons
Which sub-atomic particle did J.J. Thompson discover?
-Electrons
Explain the rutherford gold foil experiment?
- Geiger and Marsden did experiment with radioactive particles between 1908 + 1913
- They fired a beam of dense, positively charged particles (alpha particles) at very thin gold foil
- They expected particles to pass straight through gold atoms
- But some alpha particles emerged from the foil at different angles and some came straight back
- Scientists realised that the alpha particles were being repelled + deflected by a tiny concentration of positive charge in the atom
- the plum pudding model was replaced with the nuclear model of an atom
What was Niels Bohr’s ideas about an atom?
- Electrons must be orbiting the nuclues at set distances
- Electrons much be orbiting the nucleus in certain fixed energy levels (shells)
Why did Bohr revise Rutherford’s model of the atom?
-He noticed that the light given out when atoms were heated only had specific amounts of energy
When was Bohr’s model of the atom discovered?
-In 1914
How were neutrons discovered?
- In 1932 James Chadwick did an experiment that could only be explained by the existance of neutrons
- Because neutrons have no charge, it was very difficult to detect them in experiments
What are atoms made up of?
- Protons
- Neutrons
- Electrons
What is the relative charge of a proton, electron and a neutron?
- Protons have a relative charge of +1
- Electrons have a relative charge of -1
- Neutrons have no electric charge. They are neutral
What is the relative mass of a proton, electron and a neutron?
- Protons have a relative mass of 1
- Neutrons have a relative mass of 1
- Electrons have a relative mass of 0
Why do all atoms carry no overall charge?
-Because atoms contain an equal number of protons and electrons
What is the atomic number?
-Number of protons (so number of electrons)
What is the mass number?
-Number of protons and neutrons
How do you calculate the number of neutrons?
Number of neutrons = mass number - atomic number
what is an ion?
-An atom that has gained or lost electrons forming negative or positive ions
What do atoms that gain electrons form?
-Negative ions
What do atoms that lose electrons form?
-Positive ions
What are isotopes?
- Atoms of the same element with different numbers of neutrons
- They have identical chemical properties, but their physical properties, such as density, can differ
how many electrons can be fitted on each shell?
- the first shell holds up to 2 electrons
- the second shell holds up to 8 electrons
- the third shell holds up to 8 electrons
- the fourth shell holds up to 18 electrons
- 2,8,8,18
what does the outermost shell determine?
-the number of electrons on the outermost shell determines the way in which that element reacts
Who created the periodic table?
Dmitri Mendeleev
How did Mandellev proof his periodic table?
-He left gaps for the unknown elements, which when discovered matched his predictions
What are group 1 and 2 in the periodic table?
- Reactive metals: these metals react vigorously with outher elements, and most react with water
- These metals are all soft
Transition elements and their properties:
- These metals are usually very reactive
- Some like silver and gold are very unreactive
- Have high melting and boiling points
- Are hard and tough
- Have high densities
- Good conductors of heat and electricity
Noble gases and their properties:
- low boiling points
- non-metal elements
- very unreactive
- Density increases you go down
- Colourless
Group 1 - the alkali metals and their properties:
- Very reactive (stored in oil to stop reacting with oxygen in the air)
- Reactivity increases as you go down
- Low density
- Very soft
- Silvery/shiny surface when first cut
- Surface quickly goes dull as metals react with oxygen in the air. This form a layer of oxide on surface
- They form 1+ ions in reactions to make ionic compounds
- low melting + boiling temperatures for metals
- melting + boiling points decrease as you go down
- React with water to produce hydrogen and an alkaline solution containing the metal hydroxide
What does electronic structure affect?
The properties of difference groups on the periodic table
Group 7 - the halogens and their properties:
- The halogens form ions with a single negative charge in their ionic compounds with metals
- Toxic non-metals
- Low melting and boiling points
- Melting and boiling points increase as you go down
- Poor conductors of heat and electricity
- They form covalent compounds by sharing electrons with other non-metals
- Elements get less reactive as you go down
- A more reactive halogen can displace a less reactive halogen from a solution of one of its salts
