Transcript Trends ppt
Periodic Properties Chemical and physical properties of the elements change with their position in the periodic table. General Information • 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 (more protons) of the nucleus. 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 Ionic Size Distance from the center of an ion's nucleus to the edge of its electron cloud. ion Trend in Ionic Size • Cations (positively charged) – The atom has LOST electrons to become positively charged (more protons than electrons) – They are SMALLER than the neutral atom of the same element • WHY? The valence electrons are lost, along with the entire outer shell. Trend in Ionic Size • Anions (negatively charged) – The atom has GAINED electrons to become negatively charged (more electrons than protons) – They are LARGER than the neutral atom of the same element • WHY? The protons in the nucleus cannot pull in the increased Negative charge and the added electrons are repelling each other, pushing them farther apart 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? – Elements on the right of the chart want to take electrons, so they do not want to donate any. – Elements on the left of the chart would prefer to give up their electrons so it is easy to remove them. 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 positive charge of the proton has less hold on the negative charge of the electron. Electronegativity The tendency of an atom to attract electrons to itself in a chemical bond. Trend in Electronegativity • Within a period, EN increases as you move from left to right. • WHY? – Elements on the left of the period table would rather give electrons away than take another atom's electrons. – Elements on the right side of the period table only need a few electrons to complete the octet, so they have strong desire to take another atom's electrons. Trend in Electronegativity • Within a group, EN decreases as you move from top to bottom. • WHY? – Elements near the top of the period table have few electrons, so every electron is a big deal. – Elements near the bottom of the chart have so many electrons that loosing or taking an electron is not as big a deal.