Decreases from left to right across a period. More protons as you move across a period, so greater positive charge on nucleus. More electrons as you move across a period, so greater negative charge around nucleus Increasing nuclear charge pulls electrons in highest energy level closer to nucleus. Atomic Size
Atomic size increases from top to bottom within a group. Shielding effect: The increase in number of energy levels “shields” or protects electrons in the highest occupied energy levels from the attraction to protons in nucleus. Atomic Size
Increases from left to right across a period. Electrons pulled closer to nucleus and held tighter as protons are added to nucleus and electrons are added in an energy level. Trends in Ionization Energy
Second Ionization Energy Energy required to move an electron from an ion with a 1+ charge. Third Ionization Energy Energy required to remove electron from ion with 2+ charge. Easy to remove one electron from Group 1A metal, difficult to remove a second electron. So, group 1A metals tend to form ions with 1+ charge.
Electronegativity Is the tendency for an atom of an element to attract electrons from another element in a compound. How "greedy" is an element for electrons. Increases from left to right across a period. Decrease from top to bottom within a group. Francium is least electronegative and fluorine is most electronegative.
Electronegativity increases in direction of arrows Fr F
Reactivity How readily an atom reacts Reactivity differs metals to non-metals Metals are more reactive as atomic number increases down a column. o Shielding Non-metals are less reactive as atomic number increases down a column. Must consider reactivity separately for metals and non-metals.
Metals Reactivity Metals want to lose an electron to react. Therefore reactivity follows decreasing ionization energy Metals reactivity increases down an column because ionization energy decreases Metals reactivity decreases across a period because ionization energy increases.
Non-Metals Reactivity Non-metals want to gain electrons to react. Nonmetals reactivity follows increasing electronegativity. Non-metals reactivity decreases down a column. Non-metals reactivity increases across a row
Ions Ion: atom or group of atoms with a positive or negative charge. Recall: an atom is neutral because it has equal numbers of protons and electrons. Positive and negative ions form when electrons are transferred between atoms.
Ions - Positive Atoms of metals such as Na, tend to become ions by losing electrons to gain the electron config. of noble gases, forming a cation. In a sodium ion, Na +1 the number of electrons is now 10, like Neon, and is no longer equal to protons (11). Since sodium lost an electron and that electron cloud is no longer there, the atom is now smaller. Metals get smaller when they ionize.
Ions - Negative Atoms of nonmetals, tend to become ions by gaining one or more electrons to gain the electron config of noble gases and forming anions. Chlorine atoms gain one electron to have the electron config of Argon. Since chlorine now has one more electron, the atom is larger. Non-metals get bigger when they ionize