chemistry topic 1

• atomic structure
• Define an isotope

  atoms with the same number of protons and electrons but different neutrons
• Define mass number

  The mass number of an atom is the sum of protons and neutrons.
• Elements in the same group in the periodic table have the same number of electrons on the

  outer shell.
• Elements in the same period have the same number of energy levels/electron shells.
• John Dalton described atoms as tiny spheres that could not be divided
• J.J. Thomson discovered the plum pudding model

  It is a ball of positive charge with electrons embedded in the ball of positive

  charge.

  No empty space in the atom

  • Mass spread throughout
• Earnest Rutherford’s alpha scattering experiment led to the plum pudding model

  being replaced by nuclear model.

  Positive charge concentrated at the centre

  Electrons outside the nucleus

  Most of the atom is empty space

  • Mass is concentrated at the centre
• Niels Bohr adapted the nuclear model by suggesting that the electrons orbit the

  nucleus at specific distances. The electrons are on electron shells/energy level.
• The modern periodic table arranges elements in order of atomic number and groups elements with similar properties in columns called groups
• Elements in the same group have the same number of electrons in their outer shell, giving them similar chemical properties
• Elements in the same period have the same number of electron shells/energy levels, with the number of shells increasing as you go down the group
• Early periodic tables arranged elements by atomic weight. Newland's and Mendeleev's periodic tables had more than one element in a box and were missing Noble gases
• Newland's and Mendeleev's periodic tables were arranged by atomic weight. Mendeleev left gaps for undiscovered elements and predicted properties of missing elements
• Group 0 elements in the periodic table are called Noble gases, have full outer shells, and are unreactive
• The boiling points of Noble gases increase with increasing relative atomic mass as you go down the group
• Group 1 elements are called alkali metals, react with water to form alkaline solutions, and have low densities
• Group 1 metals are stored under oil to prevent them from reacting with oxygen in the air
• The reactivity of Group 1 metals increases down the group as they all have one electron in their outer shell
• Group 1 metal ions carry a charge of +1
• Observations of potassium reacting with water: forms a metal hydroxide and hydrogen gas, turns universal indicator purple
• The gas formed when Group 1 metals react with water is hydrogen
• Group 7 elements are called Halogens, have 7 electrons in their outer shell, and react by gaining one electron
• The melting and boiling points of Halogens increase as you go down the group due to increasing relative molecular mass
• The most reactive Halogen is fluorine, and reactivity decreases down the group
• A more reactive halogen can displace a less reactive halogen in a displacement reaction
• Early periodic tables, like Newland's and Mendeleev's, arranged elements in order of atomic weight
• Group 0 elements in the periodic table are called Noble gases and have full outer shells, making them unreactive
• Group 1 elements are the alkali metals, which react similarly due to having 1 electron in their outer shell
• The reactivity of group 1 metals increases down the group due to more electron shells and weaker attraction between the nucleus and outer shell electron
• The melting and boiling points of Halogens increase as you go down the group due to increasing relative molecular mass
• A more reactive halogen can displace a less reactive halogen in a displacement reaction
• Elements in the same period have the same number of electron shells/energy levels, with the number of shells increasing as you go down the group
• Both Newland's and Mendeleev's periodic tables had more than one element in a box and were missing Noble gases
• Elements in the same group have the same number of electrons in their outer shell, leading to similar chemical properties
• The modern periodic table arranges elements in order of atomic number and groups elements with similar properties together in columns called groups
• The boiling points of Noble gases increase with increasing relative atomic mass as you go down the group
• Group 1 metals react with water to form alkaline solutions and have low densities
• Advantages of Mendeleev's periodic table include leaving gaps for undiscovered elements and predicting properties of missing elements
• The most reactive Halogen is fluorine, and reactivity decreases down the group due to more electron shells and weaker attraction between the nucleus and outer shell electron