Additional Science Chemistry 2A

What is inside an atom?: Inside an atom there are 3 tiny particals: protons- Reletive mass of 1 and a charge of +. Neutrons- Reletive mass of 1 and a charge of 0. Electrons- Reletive mass of 0(too small to weigh) and a charge of -. These are called Sub-atomic particles.

The Mass nuber is the largest number on the element, in the periodic table. This represents the total mass of protons and nutrons added together(mass of atom). The Atomic Number  is the number of protons in an atom, it is also the amount of electrons in an atom.. If we take the Atomic Number away from the Mass Number then we get the number of Neutrons. In the modern Periodic Table the elements are arranged in increasing atomic number.

How ideas about the atoms have changed:Demokritos, believed that the atom was the smallest particle and could not be broken down any further, however he was wrong. "Atom" is the greek word for indivisible. Dalton described his theory of atomic properties to be: 1. All matter consists of atoms which cannot be divided up. 2. Atoms of the same element are similar howevere slighty differnt for different elements. 3.Matter cannot be created or destroyed. 4. Atoms can be formed together to make molecules. Since then our ideas have changed. 1. Electrons where discovered. 2. The atom could be split into smaller particles. 3. There is a nucleus. 4. There are protons. 5. and neutrons were discovered. As technology has improved so has our knowledge. In chemical reactions, the elements stay the same, its just the outer electrons are re-arranged. However during nuclear reactions the atom changes and creates a new substance, including alot of energy

What is an atom and what is in it?

An element is made form a spesific atom e.g. an iron magnet is made from only iron atoms. We know that an atom contains protons, neutrons and electrons. The nucleus contains the protons and neutrons, but the electrons orbit the atom in shells around the nucleus. The number of electrons in an atom will determine how it will react.

How are electrons are arranged.

Around the nucleus there are small shells , these shells  hold the electons in place. The first shell is closest to the nucleus, this shell can only hold up to 2 electrons, the next shell is called the second shell, this can hold up to 8 electrons and so can the 3rd, 4th and so on. The electrons will fill up the shells from the 1st onwards. The number of electrons in the outer shell is important as it tells us what group the element is in the periodc table. e.g. magnesium has 12 electrons, 2 in the first, 8 in the second and 2 in the third, it is in group 2. Electronic notation is a way of showing the arrangement,e.g. magnesium = 2,8,2. The first number shows how many electrons are in the first shell, the second for the number of electrons in the second shell and the third number is for the amount of electrons in the third shell. Because we know that magnesium has 2 electrons left in its outer shell we can conclude that it is in group 2 and is a metal.