Chapter 6 Periodic Trends

Organizing Elements• Chemists used the properties of elements to

sort them into groups.• Mendeleev arranged the elements in his period

table in order of increasing mass.• In the modern periodic table, elements are

arranged in order of increasing atomic number.• Periodic law stated that when the elements are

arranged in order of increasing atomic number, there is a periodic separation of their physical and chemical properties.

Organizing Elements• Recall– Groups (Families) are the columns– Periods are the row

• Representative elements are in groups 1A through 7A (1,2 and 13-17). They display a wide range of physical and chemical properties.

• the s and p sublevels of representative elements are not filled.

Organizing Elements• Representative elements include–Alkali Metals in group 1 or 1a–Alkaline Earth Metals in group 2 or 2a–Carbon Family in group 14 or 4a–Nitrogen Family in group 15 or 5a–Oxygen Family in group 16 or 6a–Halogens in group 17 or 7a

Organizing Elements• Other Families/Groups– Transition Metals in groups 3-12 or 3b to 2b

• These elements are characterized by d orbital’s that contain electrons.

– Noble Gases in group 18 or 8a• Have full p orbitals

– Lanthanide Series top row in F block– Actinide Series bottom row in F block– Inner transition metals include the Lanthanide and

Actinide Series (bottom two rows pulled out of periodic table)• These elements are characterized by f orbital’s that contain

electrons.

Classes of Elements• Three classes of elements are metals, nonmetals, and

metalloids.• Metals are good conductors of heat and electric current

– Are found on the left side of the periodic table– Metals are solid at room temperature (except mercury).– Metals are ductile (can be drawn into wires) and Malleable

(hammered in to sheets)• Nonmetals are poor conductors of heat and electric current.

– Are found on the right side of the periodic table– Solid nonmetals tend to be brittle.– Most are gases at room temperature

• Metalloids (or semi metals) have properties similar to metals and non metals. – Sit on the dark stair step line

Periodic Trends• Metallic Nature: as you move across a period

(left to right) the elements get less metallic; as you move down a group the elements get more metallic. Francium is most metallic element.

Metallic Nature INCREASES

Metallic Nature DECREASES LABEL YOUR trends

Periodic Trends• Atomic charge is the charge in the nucleus of the atom• Atomic mass the mass of the element• Both generally increase as you move across a period

and down a family

Atomic Charge and mas INCREASES

Atomic Charge and mass INCREASES

LABEL YOUR trends

Periodic Trends• Atomic radius is one half of the distance between the

nuclei of two atoms of the same elements when the atoms are joined.– In general, atomic size increases from top to bottom within a group

because you are adding energy levels (shielding effect is greater)– and decreases from left to right across a period because of effective

nuclear charge (greater pull on electrons due to addition of proton)

Atomic Radius INCREASES

Atomic Radius DECREASES

LABEL YOUR trends

What is effective nuclear charge and shielding effect?

• The effective nuclear charge is the net positive charge experienced by an electron in a multi-electron atom. – The term "effective" is used because the shielding effect of negatively charged

electrons prevents higher orbital electrons from experiencing the full nuclear charge by the repelling effect of inner-layer electrons.

• The shielding effect describes the decrease in attraction between an electron and the nucleus in any atom with more than one electron shell. – when more electrons are involved, each electron feels not only the

electromagnetic attraction from the positive nucleus, but also repulsion forces from other electrons in other shells. This causes the net force on electrons in outer shells to be significantly smaller in magnitude. Because of this these electrons are not as strongly bonded to the nucleus as electrons closer to the nucleus

Periodic Trends

• Ions is an atom or groups of atoms that has a positive or negative charge.

• Positive and negative ions from when electrons are transferred between atoms.

• Cation is an atom or groups of atoms with a positive charge that have lost electrons. – Metals form Cations

• Anion is an atom or groups of atoms with a negative charge that have gained electrons.– Nonmetals form Anions

• Group 1a forms +1 ion• Group 2a forms +2 ion• Group 3a forms +3 ion• Group 4a can form +4 or -

4• Group 5a forms -3 ion• Group 6a forms -2 ion• Group 7a forms -1 ion• Group 8 a will not react or

form ions

Fill in blanks

Periodic Trends

• Elements form Ions to achieve a noble gas electron configuration (a full outer shell)

• Full outer energy shells for MOST atoms contain 8 valance electrons.

• As metals lose electrons they form a positive charge (cation) and their radius shrinks– The greater the charge the smaller the radius

• As nonmetals gain electrons they form a negative charge (anion) and their radius expands– The greater the charge the larger the radius

Periodic Trends• Ionic radius the radius of an atom that has formed an ion

by losing or gaining electrons– In general, ionic radius increases from top to bottom within a

group because you are adding energy levels– and decreases from left to right across a period because of

the removal/addition of electrons

Atomic Radius INCREASES

Atomic Radius DECREASES

LABEL YOUR trends

Periodic Trends• Ionization energy is the energy required to

remove the first electron from an atom– First ionization energy tends to decrease from

top to bottom within a group and increase from left to right across a period.

Ionization Energy DECREASES

Ionization Energy INCREASES

LABEL YOUR trends

Periodic Trends• Electronegativity is the ability of an atom of an element to

attract electrons when the atom is in a compound. – Electronegativity values decrease from top to bottom

within a group, and values tend to increase from left to right across a period.

– MOST electronegativite element is Fluorine

Electronegativity DECREASES

Electronegativity INCREASES

LABEL YOUR trends