Transcript Period
Periodic Properties Chemical and physical properties of the elements change with their position in the periodic table. Review • Group = column • Period = row • Octet Rule – atoms tend to gain, lose, or share electrons in order to gain 8 valence electrons (full outer shell), like Noble gases – An element with a full valence shell is a happy element Atomic Size Distance from the center of an atom's nucleus to the edge of its electron cloud. atom Trend in Atomic Size • Within a period, atoms generally get smaller as you move from left to right. • WHY? Because of the increasing positive charge of the nucleus draws the electrons in more tightly. Trend In Atomic Size • Within a group, atoms generally get larger as you move from top to bottom. • WHY? Electrons are added to energy levels further from the nucleus. Dr. Lanzaflame; Atomic radii; www.monroecc.edu/wusers/flanzafame/PerRadii.pdf Ionization Energy The amount of energy needed to remove one valence electron from an atom of an element. Trend in Ionization Energy • Within a period, IE increases as you move from left to right. • WHY? – As you move from left to right the number of protons is increasing thus increasing the coulombic attraction between the nucleus and the electrons. Trend In Ionization Energy • Within a group, IE decreases as you move from top to bottom. • WHY? – The farther away from the nucleus an electron is, the easier it is to remove because the coulombic attraction is less thus the positive charge of the proton has less hold on the negative charge of the electron. Electronegativity The ability to attract an electron from another atom. Trend in Electronegativity • Within a period, EN increases as you move from left to right. • WHY? –The number of protons is increasing; therefore, the coulombic attraction is greater Trend in Electronegativity • Within a group, EN decreases as you move from top to bottom. • WHY? –The atoms are larger due to increased energy levels; therefore, the attraction for electrons would decrease Reactivity Reactivity refers to how likely an atom is to react with other substances. Trends in Reactivity • Metals – Period - reactivity decreases as you go from left to right across a period. – Group - reactivity increases as you go down a group – Why? • To react, metals needs to get rid of electrons, thus they need a low IE. Trends in Reactivity • Non-metals – Period - reactivity increases as you go from the left to the right across a period. – Group - reactivity decreases as you go down the group. – Why? • For nonmetals to react, they must gain electrons, so they need a high EN.