C1 and C2 Flashcards
(38 cards)
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
