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atoms and elements
Year 9 Science
| Term | Definition |
|---|---|
| Atomic number | number of protons |
| Mass number | number of protons + neutrons |
| Charge, Relative Mass and Location of a proton | charge = +1, relative mass = 1, location = nucleus |
| Charge, Relative Mass and Location of a neutron | charge = 0, relative mass = 1, location = nucleus |
| Charge, Relative Mass and Location of an electron | charge = -1, relative mass = 0, location = energy shell |
| number of neutrons in atom | mass number - atomic number |
| Isotope | The atoms of the same element with different mass number(different number of neutrons) |
| Plum Pudding Model ( J.J Thomson, 1904) | He discovered the electron and said the atom is a positively charged sphere with negative electrons scattered throughout it |
| Nuclear Model (Rutherford, 1911) | Rutherford discovered that atoms are mostly empty space with a small, dense, positively charged nucleus in the centre |
| Bohr Model (Niels Bohr, 1913) | Bohr proposed that electrons move around the nucleus in fixed energy levels and can gain or lose energy to move between them |
| Why was the plum pudding model rejected? | Experiments (Rutherford's) showed that atoms have a small, dense, positively charged nucleus, not positive charge spread evenly throughout the atom. |
| How is the Bohr model different from Rutherford's? | Rutherford's - Electrons orbit the nucleus in any path, but it couldn't explain atomic stability. Bohr - Electrons move around the nucleus in fixed energy levels, while absorbing and releasing energy when they jump between them. |
| How is carbon ( C-14) useful? | It allows scientists to determine the age of organic materials |
| Alpha decay | The atom loses 2 protons and 2 neutrons, so it becomes a different element. |
| Beta decay | A neutron changes into a proton, so the atom gains 1 proton and becomes a different element. |
| Gamma decay | The atom only releases extra energy. It stays the same element. |
| Why do elements in the same group have similar chemical properties? | They have the same number of valence electrons |
| Ions | Ions are atoms or groups of atoms that have gained or lost electrons, giving them a positive or negative charge. |
| Why does atomic radius decrease across a period? | The nuclear attraction increases with increase in number of electron resulting in decrease in atomic radius |
| Which metals react more strongly with water and why? | Metals lower down Group 1 because their outer electron is further from the nucleus and is easier to lose, allowing the atom to reach a stable electron arrangement more easily. |
| Where are metalloids found on the periodic table? | Along the zig-zag (staircase) line between metals and non metals |
| Atoms | the smallest unit of matter |
| Metals | Solid at room temp, shiny, good conductors of electricity and heat |
| Non - Metals | Most are gases at room temp, usually dull, and poor conductors of heat |
| Metalloids | Elements that have features of both metals and non metals |
| Atomic radius | the total distance from an atom's nucleus to its outermost orbital of electrons |
Created by:
angel_123