Exploring Periodic Trends - Mr. Ward

EXPLORING PERIODIC TRENDS ATOMIC RADIUS (AR) DEFINITION: THE DISTANCE FROM THE ATOMIC NUCLEUS TO THE OUTERMOST STABLE ELECTRON ORBITAL IN A ATOM AT EQUILIBRIUM GROUP TREND: SIZE INCREASES The number of energy levels increases as you move down a group as the number of electrons increases. Each subsequent energy level is further from the nucleus than the last. Therefore, the atomic radius increases as the group and energy levels increase. Which Atom Has The Highest AR? Li Rb K PERIOD TREND: SIZE DECREASES As you go across a period, electrons are added to the same energy level. At the same time, protons are being added to the nucleus. The concentration of more protons in the nucleus creates a "higher effective nuclear charge." In other words, there is a stronger force of attraction pulling the electrons closer to the nucleus resulting in a smaller atomic

radius. Which Atom Has The Lowest AR? Be N Atomic Radius F IONIZATION ENERGY (IE) DEFINITION: THE ENERGY REQUIRED TO REMOVE THE OUTERMOST (HIGHEST ENERGY) ELECTRON FROM A NEUTRAL ATOM IN ITS GROUND STATE. GROUP TREND: IONIZATION ENERGY DECREASES Electrons are further from the nucleus and thus easier to remove the outermost one. "Shielding" - inner electrons at lower energy levels essentially block the protons' force of attraction toward the nucleus. It therefore becomes easier to remove the outer electron WHICH ATOM HAS THE HIGHEST IE? Li Rb K

PERIOD TREND: IONIZATION ENERGY INCREASES You move across a period, the atomic radius decreases, that is, the atom is smaller. The outer electrons are closer to the nucleus and more strongly attracted to the center. Therefore, it becomes more difficult to remove the outermost electron. WHICH ATOM HAS THE LOWEST IE? Be N IONIZATION ENERGY F ELECTRONEGATIVITY (EN) Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. The Pauling scale is the most commonly used. Fluorine (the most electronegative element) is assigned a value of 4.0, and values range down to cesium and francium which are the least electronegative at 0.7 GROUP TREND: ELECTRONEGATIVITY DECREASES This is because atomic number increases down a group, and thus there is an increased

distance between the valence electrons and nucleus, or a greater atomic radius. WHICH ATOM HAS THE HIGHEST EN? Na K Fr PERIOD TREND: ELECTRONEGATIVITY INCREASES If the valence shell of an atom is less than half full, it requires less energy to lose an electron than to gain one. Conversely, if the valence shell is more than half full, it is easier to pull an electron into the valence shell than to donate one. WHICH ATOM HAS THE LOWEST EN? Li Al F ELECTRONEGATIVITY IONIC RADIUS (IR) SIZE OF AN ION CATIONS: A POSITIVE ION IS FORMED THEY LOSE THE NEED TO USE AN ENERGY LEVEL THEREFORE THE ION IS SMALLER THAN THE NEUTRAL ATOM ANIONS:

A NEGATIVE ION IS FORMED SINCE THEY HAVE MORE NEGATIVE CHARGES THAN POSITIVE CHARGES THE EXTRA IONS ARE REPELLED AWAY FROM EACH OTHER AND THEREFORE THE ION IS LARGER THAN THE NEUTRAL ATOM. PRACTICE WHAT ION WITH THE FOLLOWING ATOMS FORM? CA N RB AL AS O WHICH IS SMALLEST IN EACH GROUP? C+4 C

NA NA+1 N N-3 FE FE+3 C-4

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