PERIODIC TRENDS Chapter 6

VALENCE ELECTRONS Electrons in an atom’s highest principle energy level Valence electrons determine the chemical properties of an element Atoms in the same group have similar properties because they have the same number of valence electrons Energy level of valence electrons is indicated by the period in which the element is found

IONS Neutral atoms have no overall electrical charge because – they have equal numbers of positively charged protons in the nucleus and negatively charged electrons surrounding the nucleus. Noble gases have stable configurations because – the s and p orbitals of their highest energy level are filled, forming a stable octet. Exception: helium has only two s e– in its highest energy level

IONS Atoms gain or lose electrons to – increase stability by attaining electron configurations similar to noble gases. Such an atom is no longer neutral but has become a charged particle known as an ion. Metals: lose electrons to become cations (+) Nonmetals: gain electrons to become anions (–)

OXIDATION NUMBERS Definition: the positive or negative charge of a monatomic ion. It equals the number of electrons transferred when an atom forms its ion. Predicted by the group of an element + when electrons are lost; –when electrons are gained Written above group number on periodic table Noble gases have oxidation number of zero: they do not transfer electrons and do not form ions Elements in carbon group have no oxidation number; they do not typically form ions

ATOMIC RADII DECREASES One half the distance between the nuclei of two adjacent atoms of the same element Trend across the period (left to right) Atomic radius DECREASES Trend within the group (bottom to top) The General Trend DECREASES

IONIC RADII One half the distance between the nuclei of two adjacent ions of the same element Metal atoms tend to ____ electrons to become ______ (________ ions) Therefore, cations are smaller than their corresponding atoms Nonmetal atoms tend to ____ electrons to become ______ (________ ions) Therefore, anions are larger than their corresponding atoms lose cations positive gain anions negative

IONIC RADII One half the distance between the nuclei of two adjacent ions of the same element Trend across the period (left to right) Ionic radius DECREASES Trend within the group (bottom to top) The General Trend DECREASES

IONIZATION ENERGY INCREASES The minimum amount of energy required to remove an electron from an atom Trend across the period (left to right) Ionization Energy INCREASES Trend within the group (bottom to top) The General Trend INCREASES

ELECTRONEGATIVITY INCREASES The relative ability of an atom to attract electrons Trend across the period (left to right) Electronegativity INCREASES Trend within the group (bottom to top) The General Trend INCREASES

REACTIVITY Refers to how readily chemical substances undergo chemical reaction Related to several factors, including the number of valence electrons, ionization energy, and electronegativity Metals: more reactive with low numbers of valence electrons and low ionization energies Nonmetals: more reactive with larger numbers of valence electrons and high electronegativity values

REACTIVITY DECREASES INCREASES Trend across the period (left to right) Reactivity of metals DECREASES Reactivity of nonmetals INCREASES Trend within the group (bottom to top) DECREASES INCREASES