PERIODIC TRENDS WHAT IS A PERIODIC TREND? • A PATTERN OF CONSTANT INCREASE OR CONSTANT DECREASE ACROSS A PERIOD AND DOWN A GROUP. ATOMIC RADIUS • ATOMIC RADIUS INCREASES ACROSS A PERIOD FROM RIGHT TO LEFT AND INCREASES DOWN A GROUP. • AS PROTONS ARE ADDED ACROSS A PERIOD, SO ARE ELECTRONS, BUT THE PULL OF THE PROTONS IS GREATER THAN ELECTRON REPULSION, SO THEY ARE PULLED INWARD AND THE ATOMIC SIZE DECREASES. • AS YOU GO DOWN A GROUP, YOU ADD NEW LAYERS OF ELECTRONS. EACH SHELL REPELS THE OTHERS, AND ATOMIC SIZE INCREASES. IONIZATION ENERGY • IONIZATION ENERGY INCREASES FROM LEFT TO RIGHT ACROSS A GROUP AND FROM BOTTOM TO TOP OF THE PERIODIC TABLE. • AS ATOMIC SIZE DECREASES, THE ELECTRONS ARE HELD MORE TIGHTLY. THIS MEANS IT TAKES MORE ENERGY TO BREAK THEM OFF THE ATOM. ELECTRONEGATIVITY • ELECTRONEGATIVITY INCREASES LEFT TO RIGHT ACROSS A PERIOD AND FROM BOTTOM TO TOP OF THE TABLE. • AS ATOMS BECOME SMALLER, THEY HOLD MORE TIGHTLY TO THEIR ELECTRONS. THE ELECTRONS CAN FEEL THE NUCLEAR PULL MORE STRONGLY, SO THEY ARE PULLED TOWARD THE NUCLEUS. SMALLER ATOMS • IN SMALLER ATOMS, THERE ARE FEWER ELECTRONS SO THERE ARE FEWER ELECTRON REPULSIONS. THIS ALLOWS THE ELECTRONS TO “FEEL” THE NUCLEUS’ PULL AND PULLS THEM INWARD, SHRINKING THE ATOM. LARGER ATOMS • LARGER ATOMS HAVE MORE LAYERS OF ELECTRONS. THEY REPEL EACH OTHER, INCREASING THE DISTANCE OF EACH LAYER AWAY FROM THE NUCLEUS. THEY CANNOT “FEEL” THE NUCLEUS AS WELL AND SO DO NOT GET PULLED IN. THIS MAKES THE ATOM BIGGER.
