Flashcards in C4a Deck (22):
What does an atom have?
A nucleus surrounded by electrons.
A very small mass and a very small size.
What charge does a nucleus, an electron and an atom have?
A nucleus is positively charged, an electron is negatively charged and an atom is neutral.
What is the nucleus made up of?
Protons and neutrons.
What is the relative charge and relative mass of an electron, a proton and a neutron?
Electron charge -1 and mass 0.0005 (zero)
Proton charge +1 and mass 1
Neutron charge 0 and mass 1
Why is an atom neutral in terms of its subatomic particles?
Atoms contain three sub-atomic particles called protons, neutrons and electrons. The number of electrons in an atom is always the same as the number of protons, so atoms are neutral overall. The charge on the electrons is the same as the charge on the protons, but opposite - so the charges cancel out.
What is the approximate radius and mass of atoms?
Radius 10-10 m
Mass 10-23 g
How can you identify the atomic number of an element by using a periodic table?
It is always the smallest number, in the bottom left.
What is the atomic number?
The number of protons in an atom.
What is the mass number?
The total number of protons and neutrons.
Always the biggest number.
What are isotopes?
Varieties of an element that have the same atomic number but different mass numbers. So the same number of protons but a different number of neutrons.
How do you deduce the number of protons, electrons and neutrons in a particle given its atomic number and mass number?
The atomic number gives the number of protons and electrons. The number of neutrons is the mass number minus the number of protons.
So for carbon 12 which has an atomic number of 6 and a mass number of 12, there are 6 protons and electrons and 6 neutrons.
How do you identify isotopes from data about the number of electrons, protons and neutrons in particles?
Atoms of the same element will have the same number of protons - these are isotopes.
Why is a substance an element or a compound given its formula?
Elements are represented by one or two letters. The first letter is always a capital and the second is always lower case. Compounds are represented by formulae. Symbols and numbers show the atoms in the compound.
For example: ZnCO3 is the formula of zinc carbonate.
Compounds contain at least two elements.
What is the arrangement of elements in the periodic table?
The elements are in order of ascending atomic number.
Elements with similar properties form columns. These vertical columns are called groups.
The group to which the element belongs corresponds to the number of electrons it has in its outer shell. E.g. group 1 elements have 1 outer shell.
The rows are called periods. Each new period represents another full shell of electrons. The period to which the element belongs corresponds to the number of shells of electrons it has.
How do you deduce the number of occupied shells or the number of electrons from the electronic structure of an element?
The number of occupied shells is the same as the period number(row in the table)
The number of electrons in the outer shell is the same as the group number (column in the table)
How can you deduce the electronic structure of the first 20 elements in the periodic table?
The periodic table tells you how many electrons an element has.
The electron shell rules tell you that the first shell can only take two electrons, the second shell 8 and the third shell 8.
So for nitrogen which has 7 protons so 7 electrons, its electronic structure is 2, 5 which add up to 7.
For calcium which has 20 protons so 20 electrons, its electronic structure is 2, 8, 8, 2 which add up to 20.
What are the main stages simply described in the development of atomic structure?
start of 19th century - John Dalton - solid spheres
1897 - J J Thompson - plum pudding model
1909 - Ernest Rutherford/ his students Hans Geiger and Ernest Marsden - gold foil experiment/nuclear atom theory.
Niels Bohr - electrons exist in fixed orbits
What was Dalton's theory?
He described atoms as solid spheres, and said that different spheres made up different elements.
What was Thomson's theory?
He concluded from his experiments that atoms weren't solid spheres. His measurements of charge and mass showed that an atom must contain even smaller, negatively charged particles - electrons. The new theory was known as the 'plum pudding model'.
What was Rutherford's theory?
Conducted with his students Geiger and Marsden gold foil experiment. They fired positively charged particles at an extremely thin sheet of gold. from the plum pudding model they were expecting most of the particles to be deflected by the positive 'pudding' that made up most of an atom. Most of the particles passed straight through the gold atoms, and a very small number were deflected back. So the plum pudding model couldn't be right.
So Rutherford came up with an idea that could explain this new evidence - the theory of the nuclear atom. In this, there's a tiny, positively charged nucleus at the centre, surrounded by a 'cloud' of negative electrons - most of the atom is empty space.
What was Bohr's theory?
Scientists realised that electrons in a 'cloud' around the nucleus would be attracted to the nucleus, causing the atom to collapse. Bohr proposed a new model of the atom where all the electrons were contained in shells. Bohr suggested that electrons can only exist in fixed orbits, or shells, and not anywhere in between. Each shell had a fixed energy. His theory was accepted by many experiments and it helped to explain lots of other scientists' observations at the time.