Periodic Trends 6.3

Atomic Radius The distance between an atom’s nucleus and its valence electrons. How closely an atom lies to a neighboring atom Size of the atom varies from substance to substance

Trends within Periods Atomic Radii DECREASE as you move left to right across a period Because of Increased nuclear charge(total charge of all protons in the nucleus) Increased nuclear charge pulls the outermost electrons closer to the nucleus & decreases the atomic radius.

Trends within Groups Atomic Radii INCREASE as you move down a group. Nuclear charge increases and electrons are added to higher energy levels. Moving down a group: The Outermost orbital increases in size Increasing principal energy level

Examples Which element has the smallest atomic radius? Largest atomic radius? Iodine (I) Bromine (Br) Fluorine (F) Chlorine (Cl) Fluorine Iodine

Ionic Radius Ion- an atom that gains or loses electrons When atoms lose electrons they form positive ions and become smaller The electron lost will always be a valence electron Loss of valence electrons may leave an empty outer orbital which results in a smaller radius Repulsion between fewer electrons decreases allowing them to be pulled closer to the nucleus

When atoms GAIN electrons they form negative ions and they always become larger. Increase of an electron to an atom increases the repulsion between the valence electrons forcing them to move farther apart. This equals larger radius

Ionic Radius within Periods Size of the positive ions gradually decreases Beginning in group 5A or 6A the size of the much larger negative ions also gradually decreases. Ionic Radii DECREASE across periods

Ionic Radius within Groups As you move down a group an ion’s outer electrons are in higher principal energy levels resulting in a gradual increase in ionic size Ionic Radii increase as you move down a group

Ionization Energy The energy required to remove an electron from an atom “How strongly an atom’s nucleus holds on to its valence electrons” High IE indicates atom has a strong hold on its electrons Low IE indicates an atom loses its outer electron easily

Ionization Energy Energy required to remove the 1st electron is the first ionization energy. Energy required to remove the 2nd electron is the second ionization energy.

Ionization Energy within Periods INCREASE as you move from left to right across a period The increased nuclear charge of each successive element produces an increased hold on the valence electrons.

Ionization Energy within Groups DECREASE as you move down a group Occurs because atomic size increases as you move down a group With the valence electrons farther from the nucleus less energy is required to remove them

Octet Rule Atoms tend to gain, lose, or share electrons in order to acquire a full set of eight valence electrons. Elements on the right side of the periodic table tend to gain electrons in order to acquire the 8 valence electrons. (Form negative ions) Elements on the left side of the periodic table tend to lose electrons and form positive ions.

Electronegativity of an Element Indicates the relative ability of its atoms to attract electrons in a chemical bond Noble Gases are not assigned values Fluorine is the most electronegative Fr & Cs are the least In a chemical bond the atom with the greater electronegativity more strongly attracts the electrons

Electronegativity Trends within Periods & Groups INCREASES as you move across a period DECREASES as you move down a group The lowest electronegativities are found at the lower left side Highest are found at the upper right side

Example Problems Which element has the highest electronegativity? Lowest? N- Nitrogen P- Phosphorus As-Arsenic Sb-Antimony Bi- bismuth N=highest Bi= Lowest

Homework Problems Pg. 175 #56, 57, 59, 62, & 63