Chemistry Glossary • Pure substances – when only one type of element or compound is found in a substance. • Mixture – when more than one element or/and compound is together in a substance. • Element – made up of only one type of atom • Compound – when 2 or more different atoms are bonded together • Molecule – more than one element covalently bonded to another atom.
Chemistry Glossary • Physical Changes-When no new substance is formed only the appearance might change. E.g. when ice is heated it turns into liquid • Chemical Changes – when a new substance is formede.g. when Mg metal is heated it reacts with oxygen to form magnesium oxide (white pow • http://www.youtube.com/watch?v=RcR1CE902Foder).
History of Atomic Structure • http://www.youtube.com/watch?v=vUzTQWn-wfE
The Ancient Greeks Hey Spiros! I reckon everything’s made up of lit bits called atoms. They’re so small you can’t even see them. Rubbish Democritus! What’s wrong with the “earth, air, fire and water” theory? Democritus an ancient Greek philosopher, proposed that all matter was made up of tiny, invisible particles.
John Dalton John Dalton proposed that an element was composed of identical, invisible atoms characteristic of that element and no other (billiard ball model)
John Joseph Thomson J.J. Thomson’s identification of the electron showed that atoms were not indivisible. Thomson proposed that an atom consisted of a soft, positively charged jelly-like sphere into which negatively charged electrons were embedded, like plums in a pudding. (plum pudding model)
Ernest Rutherford Rutherford proposed that an atom consisted mainly of empty space. Most of the mass and all the positive charge electrons would be concentrated in the centre, which he called the nucleus. Negatively charged electrons would occupy the space around the nucleus (nuclear model).
James Chadwick Chadwick identified a particle in the nucleus that had almost the same mass as a proton but no charge. It was called a neutron, and abbreviation for a neutral proton.
Atomic Structure • Atoms are made up of: • Positive charge called the PROTON • Negative charge called the ELECTRON • Neutral charge called the NEUTRON
Atomic Structure Atomic Number = Number of protons Mass number or Atomic Number= Number of Protons + Neutrons Atomic Weight = Average Atomic Weight of that atom found in nature. This is usually a decimal number. In a neutral atom the umber of Protons = Number of electrons
PERIODIC TABLE • http://www.webelements.com/ • Handout • Last page of text book
Activity Use your periodic table to identify the symbol for the following and draw them in your book • Hydrogen • Carbon • Oxygen • Helium • Fluorine • Sodium
Atomic Size If all the atoms of the Earth were compressed to remove the empty spaces in them , then they would be able to fit in a suitcase.
Atomic Size Look at the dot on this page. If you lined up some oxygen atoms in a line across the dot there would be 7,000,000 oxygen atoms in a line .
Atomic Size If every molecule in a tumbler of water could be changed into a grain of sand, the sand so produced would be enough to cover Australia 35 metres deep.
Atomic Size If you poured the Coke from a 1.25 litre bottle out at 1 million molecules per second it would take about 750,000,000 years to empty it.
Atomic Structure • But there is more to the story…. • After Rutherford….
Niels Bohr Bohr suggested that an atom could have only certain, definite energies, corresponding to its electrons being in certain definite orbits. The electrons could be compared to a solar system with its planets in definite orbits around the sun.
How are electrons arranged around the nucleus? Electrons orbit the nucleus in paths called rings or shells. Hydrogen and Helium have one electron shell. All other atoms have two or more shells.
How are electrons arranged around the nucleus? Each shell is named with a capital letter. The first shell is called the “k” shell. It is closest to the nucleus. The next shell is the “L” shell. The “M” shell comes next. And so on.
How are electrons arranged around the nucleus?(*only for first 20 elements of periodic table) Each shell can hold only a certain number of electrons. • The “K” shell can hold 2 electrons • The “L” shell can hold 8 electrons. • The “M” shell can hold 8 electrons*. What element does this model represent?
How are electrons arranged around the nucleus?(*only for first 20 elements of periodic table) The number of shells an atom has depends upon its number of electrons. Each shell must have its full number of electrons before a new shell starts. If there are more electrons than a shell can hold, a new shell starts.
How are electrons arranged around the nucleus?(*only for first 20 elements of periodic table) Handout activity
Resources • “Elementary Atoms” – W. Irwin 1993 • “Chemical connections” Uncertain of date, publishe and author