ATOMS #4: PERIODIC TABLE
- WACADEMY
- Dec 20, 2023
- 3 min read
ATOMS #4: PERIODIC TABLE
PERIODIC TABLE
^What to catch from the above slides:
Modern periodic table (the ones we use today) is organized based on their ATOMIC NUMBER. It would also be correct to say the table is organized based on their electronic configuration (see "ATOMS #3: ELECTRONIC CONFIGURATION")
Groups are vertical COLUMNS of the periodic table
Periods are horizontal ROWS of the periodict table
The primary groups you should be familiar with are Groups 1 & 2 (Alkali metals & Alkaline Earth Metals) which obviously have METALLIC PROPERTIES
Groups 17 & 18 (Halogens & Noble gases) have non-metallic properties
^All elements inherently want to achieve the stability Noble Gases have, thus:
Metals like to LOSE ELECTRONS
Non-metals like to GAIN ELECTRONS
PERIODIC TRENDS
^These 2 images are all you need to know for periodic trends, which are frequently tested material:
Atomic radius: refers to size of atoms. They decrease from left to right of the periodic table because there are more protons (more + charge) pulling at the electrons, drawing them near to the nucleus. They increase from top to bottom because there are more energy shells as you go down the periodic table (n= 1,2,3,4,...)
Metallic character: it increases as you go left and down the periodic table. This is quite obvious with how alkali metals and alkaline earth metals are positioned on the left side of the periodic table. Now just for extra understanding, metallic character increases down the column because it is easier to LOSE electrons as the nuclear (proton) charge the valence electrons feel is less when they are at higher energy shells (n), which is the case as you go down the column.
Non-metallic character: it increases as you go right and up the periodic table contrary to the metallic character.
Zeff: It increases as you go right and up the periodic table. Zeff essentially refers to the nuclear charge valence electrons feel (Zeff = Z - S). Now "Z" refers to total nuclear charge, and "S" refers to shielding (or interfering) by core electrons, preventing valence electrons from being fully exposed to the total nuclear charge.
Ionization Energy (IE): It increases as you go right and up the periodic table. This is because the nuclear charge increases as you go from left to right as the atomic number (Z) or # of protons increases. This pulls on valence electrons more strongly, thereby making it hard to remove the valence electrons. IE refers to energy required to remove one valence electron.
Electron affinity (EA): It increases as you go right and up the periodic table. EA basically means "how inclined is the atom to gain an electron?" Atoms that readily gain electrons are represented by a negative value, and those that resist gaining electrons are usually assigned positive values. Since non-metals like to gain electrons, EA will increase towards where atoms exhibit more non-metallic properties.
Polarizability: It increases left and down the periodic table. Polarizability is a measure of how easily an electron cloud is distorted by an external source like an electric field, meaning the more electrons you have, the higher chance it will be distorted. The reason it increases from right to left is because the valence electrons are less tightly bound by the nuclear charge as you go from right to left.
FURTHER UNDERSTANDING OF PERIODIC TRENDS
^What to catch from the above slide:
Take a look at the example of 1st and 2nd IE of magnesium, and how IE2 is greater than IE1. IE1 = IE when removing first valence electron; IE 2 = IE when removing 2nd valence electron.
The reason IE2 is greater is because the nuclear charge is now distributed among fewer number of electrons (since one valence electron has already been removed from IE1). This means the effective nuclear charge is greater for each electron and thus it will require more energy to remove the 2nd electron.
^What to catch from the above slide:
When you compare EA of a neutral atom and an anionic atom, EA would obviously be more favourable towards the neutral atom as it will be more INCLINED TO gain an electron than an atom that already has gained an electron. An anion's electron will exert a repulsive force, making the EA value positive (which is considered a LOW ELECTRON AFFINITY value)
^What to catch from the above slide (THIS ONE IS ALWAYS TESTED**):
If we are given the same atom, the atomic radius or size of it will differ based on their states. By states, I mean, "are they in cation, anion or neutral form?"
The rule of thumb is: ANION > ATOM (NEUTRAL) > CATION. This is because the extra electron in an anion will distribute the nuclear charge over more electrons, making them less tightly bound, thus bigger size. The cation is smaller because the loss of one electron will have the nuclear charge distribute itself among FEWER electrons, thereby more tightly binding them all together.
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