# PERIODIC TABLE TRENDS. PERIODICITY A regular pattern in the properties of elements Also called a “TREND” Some properties are similar due to the valence.

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PERIODIC TABLE TRENDS

PERIODICITY A regular pattern in the properties of elements Also called a “TREND” Some properties are similar due to the valence e - ’s  specifically in groups of element Remember  the main group elements, Roman numerals on the top tells us the number of valence e -

some properties of elements are related to the positive attraction of the nucleus for electrons called nuclear effective charge This attraction is due to electrostatic attraction and is dependent on quantity of the charge as well as the distance separating the charge Example: quantity + + + - - + Greater attraction distance +- +- Greater attraction

Atomic Radius Can’t know the exact size of an atom  can only look at relative size Atomic radius is defined as the closest distance to which one atom will approach another atom of any other size

In a period, atomic radius decreases as atomic number increases (from left to right in a row) WHY? As atomic number increases, the increasing number of protons attract the valence electrons closer to the nucleus  decreasing the size of electron cloud Elements in the same period have valence e- in the same valence shell  the effective nuclear charge is “felt” more by the valence e- across a period

In a group, atomic radius increases as atomic number increases (from top to bottom) WHY? As atomic number increases in a group, each successive element has its valence electron farther from the nucleus (since they are placed in a higher energy level with each successive element)  the effective nuclear charge has less of an effect on the valence e- and the size of the atom increases

SUMMARY Atomic radius from top to bottom in any group Atomic radius from left to right in any period increases decreases

IONIZATION ENERGY AND TRENDS Ionization energy (I.E.) Amount of energy required to remove an electron from a gaseous atom I.e. X (g) + I  X + (g) + e - it is an endothermic process  The amount of energy required to remove ONE e - from a gaseous atom is called the first ionization energy (I 1 )  The amount of energy required to remove a SECOND e - from a positive ion is called the second ionization energy (I 2 )

Each successive ionization requires more energy because as electrons are being removed, the nuclear effective charge has a greater pull on the electrons In a period, I.E. increases as atomic number increases WHY? As the nuclear charges increases across a period, it becomes more difficult to remove electrons  more energy is required to remove them

In a group, I.E. decreases as atomic number increases WHY? With every successive element in a group there is an additional energy level of electrons so the electrons are at a greater distance from the nucleus This means it is easier to remove electrons since not much energy is required to remove them Also, the shielding effect of the kernel electron makes the valence e- feel less attracted to the nucleus

SUMMARY I.E. across a period I.E. down a group increases decreases

ELECTRON AFFINITY AND PERIODICITY Electron affinity (E.A) The amount of energy released when a gaseous atom accepts an electron to form an anion. (a negatively charged atom) i.e. X (g) + e -  X - (g) + Energy It is an exothermic process Adding the first e - is an EXOTHERMIC process Adding a second e- is ALWAYS an ENDOTHERMIC process

Adding 2e - at the same time would still be an ENDOTHERMIC process I.e. O (g) + 2e - + energy  O 2- (g) In general, Electron Affinity as atomic number increases in a PERIOD The Electron Affinity as atomic number increases in a GROUP Electron affinity is the OPPOSITE of an atom’s ionization energy increases decreases

WHY? The more attracted the element is for electrons, the more energy it will release when it accepts an e - MOST reactive  Fluorine (in terms of E.A)

 ELECTRONEGATIVITY  The measure of the ability of an atom to attract SHARED electrons to itself  Electronegativity is much higher for non-metals than metals  In a period, the electronegativity will increase as the atomic number increases  In a group, the electronegativity will decrease as the atomic number increases

 WHY? The stronger the pull of the nucleus for electrons, the higher the value of electronegativity

REACTIVITY The alkali metals are the most reactive metals and the halogens are the most reactive non-metals Reactivity increases as one moves away from the group containing Zn on the periodic table (transition metals are fairly unreactive when compared to the main group elements) For metals, reactivity increases down a group but for non-metals, increase going up a group

METALLIC CHARACTER Metals are located on the left side of periodic table and non metals are on the upper right side of the table Elements tend to posses more metallic character as one moves to the lower left corner of the periodic table Fr is the most metallic element and He is the most non-metallic element

According to this trend, which transition metal is the least metallic? Zn

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