Periodic Trends Each horizontal row is called a period because it corresponds to one full cycle of a trendEach horizontal row is called a period because it corresponds to one full cycle of a trend A trend is just a pattern that goes across or up and down the periodic tableA trend is just a pattern that goes across or up and down the periodic table These trends occur because all atoms follow the octet rule:These trends occur because all atoms follow the octet rule: All elements gain or lose electrons so they wind up with the same electron configuration as the nearest noble gas All elements follow this rule because having full valence shells makes elements very stableAll elements follow this rule because having full valence shells makes elements very stable There are 3 main patterns of the periodic tableThere are 3 main patterns of the periodic table

ATOMIC RADIUS Atomic Radius is half the distance between two nuclei of the same element when bonded together Radius decreases from left to right, increases as you move down a group As we go down a group each atom has an additional electron shell, so the atoms get bigger. Going from left to right across a period, the size gets smaller. Electrons are in the same energy level but there is more nuclear charge so outermost electrons are pulled closer –Remember as we move across a period we are adding protons and electrons so the attraction between them is much stronger

ELECTRONEGATIVITY Electronegativity is a measure of how strong an atom will pull electrons away from other atoms it has bonded to The octet rule states that elements on the left side of the periodic table want to lose electrons while those on the right side want to gain electrons. –Electronegativity increases as you move from left to right across the periodic table. –As you move from left to right atoms of the different elements are more likely to gain electrons

ELECTRONEGATIVITY As you move down a group, the farther the electrons are away from the nucleus, plus the more electrons an atom has. Thus, more willing to share. giving these elements a low electronegativity –Shielding effect occurs as more electrons become present electrons repel each other

Metals vs Non-Metals Metals are at the left of the table. They let their electrons go easily giving them a low electronegativity At the right end are the nonmetals. They want more electrons. Try to take them away from others giving them a high electronegativity.

IONIZATION ENERGY This is the amount of energy required to pull one electron (e-) off of an atom –The amount of energy depends on the shell the atom is on As you move from left to right across the periodic table, the energy required to remove an electron increases because of the octet rule –Remember that all elements want to gain or lose electrons to be like the nearest noble gas Elements on the left side like lithium (Li) want to lose e- to be like the nearest noble gas. As a result it doesn’t take much energy to pull an electron off of the atom since it wants to lose an e- anyway. Elements on the left side have a low ionization energy. Elements on the right side such as fluorine (F) want to gain e-, so it takes a high amount of energy to remove one. Elements on the right side have a high ionization energy

IONIZATION ENERGY –The noble gases have the highest ionization energy, meaning it takes the most energy to remove one of their e-. If you think about it this makes sense since noble gases are stable and all elements want to become and remain stable. (octet rule) –Ionization energy decreases as you move down a group in the periodic table The reason is that e- in low energy shells repel e- in the higher energy shells because they are both negatively charged. (shielding effect) As a result of this shielding effect e- in lower energy shells are more tightly bound to the nucleus than e- in higher shells.

REMEMBER: As you move down groups you are adding on energy levels –If you move down a group each element will have one more energy level but it will have the same number of valence electrons as the previous element

REMEMBER: As you move horizontally along a period (going up by atomic number) the number of energy levels will remain the same –Each element will have one more valence electron than the previous element.