One day, I should go back and add pictures to this blog post. I can't be bothered today though.
Compare the relative charge and relative masses of protons, neutrons and electrons
Atoms are made up of three main particles: protons, neutrons and electrons. (I'm pretty sure that these particles are actually made up of even smaller particles, like protons are made up of a positron and a neutron or something along those lines, but let's not go there.) Positively-charged protons and neutrally-charged neutrons have about the same mass and they stick together in the nucleus in the centre of the atom.
Surrounding the nucleus is an "electron cloud" where all of the electrons hang out, orbiting the nucleus or whatever it is they do there. Electrons are negatively charged and their mass is 1/2000th of that of a proton or a neutron. In an atom, the number of electrons is equal to the number of protons. This keeps the positive and negative charges equal and the overall charge on the atom is neutral.
Identify elements using their atomic number (Z)
The main difference between elements is how many protons are located in their nuclei. The atomic number (or Z) of an element is given by how many protons are in the nucleus of an atom. Therefore, the atomic number and the type of element are related. Any atom with an atomic number of 1 (and therefore only one proton in the nucleus) is a hydrogen atom. Any atom with an atomic number of 2 (and therefore two protons in the nucleus) is a helium atom. And so on.
Explain isotopes using their atomic number (Z) and mass number (A)
Although all atoms of one element have to have the same number of protons, they do not necessarily have to have the same number of neutrons. Atoms with the same number of protons and a different number of neutrons are called isotopes. Examples of isotopes include Carbon-12 and Carbon-14.
Mass number, or A, is the sum of the protons and neutrons of an element. On the periodic table, you might notice that the mass number of most elements is not a whole number. This is because it is the average mass of an atom of that element, taking into consideration all of the isotopes of that atom and how common they are.
Carbon has 6 protons. Carbon-12 has 6 protons and 6 neutrons (6 + 6 = 12). Similarly, Carbon-14 has 6 protons and 8 neutrons (6 + 8 = 14). The mass number of carbon, as listed on the periodic table, is 12.01. This is because Carbon-12 is much more common than Carbon-13 or Carbon-14.
Use the energy level or shell model of electron structure to write the electron configurations for the first twenty elements
As I said before, the electrons are located in an electron cloud which surrounds the nucleus. However, they aren't all located in the same place in this electron cloud. The electron cloud is divided up into different shells, or energy levels, which hold different numbers of electrons. The first energy level, K, can only hold 2 electrons. When it's full, the next lot of electrons start moving into the second energy level, L. L can only hold 8 electrons. When it's full, electrons start moving into the energy level M. M can actually hold up to 18 electrons, but after the 8th electron, subsequent electrons move into shell N instead. Shell M only gets filled up as you progress through the transition metals.
Writing electron configurations is simple. Just write the number of electrons in each shell. Let's take potassium as an example. Potassium has 19 electrons. The first two will go in energy level K, the next 8 in energy level L, the next 8 in energy level M and then the last one will go in energy level N even though M isn't full yet (due to that strange rule that I mentioned before). Therefore, the electron configuration of potassium is as follows:
2, 8, 8, 1
In 2AB Chemistry you only need to go up to Calcium, which is the element right before the transition metals, so you don't need to worry about backfilling shell M too much just yet.
Explain the relationship between position on the Periodic Table and number of valence electrons of elements in groups 1-2 and 13-18
Valence electrons are basically the electrons in the outer shell of an atom. They contribute to the chemical properties of an atom.
Electrons with one valence electron are located in group 1 of the periodic table, and electrons with two valence electrons are located in group 2. Then electrons with 3-8 valence electrons are located in groups 13-18 of the periodic table, respectively. The periodic table is actually quite an ingenious invention.
Explain the relationship between the number of valence electrons and chemical properties of elements in groups 1-2 and 13-18
As I mentioned before, valence electrons contribute to the chemical properties of an atom. You see, all atoms want to attain a stable configuration of a full outer shell (either 2 or 8 valence electrons). This is the same configuration as the elements in group 18.
Since the elements in group 18 already have the electron configuration that they want, they are relatively non-reactive and tend not to form bonds with other elements. Elements that are very close to having a full outer shell (Groups 1 and 17), however, are a different story.
Group 1 elements only have one valence electron. If they lose this valence electron, then they'll be happy. Group 1 elements with more electrons and therefore more shells tend to be more reactive as their one valence electron will be further away from the nucleus and therefore not as strongly affected by the positively-charged protons in the nucleus.
Group 17 elements have 7 valence electrons. If they gain just one electron, they'll be happy. Group 7 elements with fewer electrons and therefore fewer shells tend to be more reactive as the positively-charged protons can more easily attract electrons without too many electron clouds in the way.
Group 2 and 13 elements also lose electrons while group 15 and 16 elements gain electrons. Group 14 elements are a different story, however. It may seem that they can either lose or gain four electrons, which some do occasionally, but more often than not, they tend to share electrons with non-metal elements, forming extremely strong bonds.
Explain the formation of positive and negative ions for elements in groups 1-2 and 13-18
As I said before, group 1, 2 and 13 elements tend to lose 1, 2 or 3 electrons in order to get a full outer shell and become stable. The loss of electrons means that there are now more protons than electrons, and therefore more positive than negative charges. The atoms are now positively charged ions. If one electron is lost, the atom is a +1 ion. If two electrons are lost, the atom is a +2 ion and so on.
Elements in groups 15, 16 and 17, on the other hand, tend to gain 3, 2 or 1 electrons in order to get a full outer shell. Gaining electrons means the formation of negative ions rather than positive ions. Gaining 3 electrons makes a -3 ion, gaining 2 makes a -2 ion, and so on.
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