Wow, that periodic table is useful. Electrons and Periodicity

Arrangement of the Modern Periodic Table In the modern periodic table, the elements are organized into groups (vertical columns) and periods (horizontal rows) in order of increasing atomic number. Groups are also called FAMILIES since they are similar in chemical properties.

Groups are numbered 1–18 or 1–8 with A/B notation Tall columns are notated as “A” Main group elements Short columns are notated as “B” Numbering Groups 1A 2A3A 4A 5A 6A 7A 8A3B 4B 5B 6B 7B 8B 1B 2B Main Group Elements

Step-wise line that begins at the element boron and moves downward in a zigzag pattern divides the table Metals are to the left of the line Nonmetals are to the right of the line Along the line are the metalloids Possess properties of both metals and nonmetals Metals, Nonmetals, and Metalloids Metalloids

Properties of Metals 1. They are malleable, ductile, and have luster. 2. They are good conductors of heat and electricity. 3. They have relatively high densities. 4. They are solids at standard temperature and pressure (STP), except for mercury, which is a liquid.

Properties of Nonmetals They are dull and brittle. They don’t conduct heat and electricity well. They have relatively low boiling and freezing points. They exist in all phases at STP, but most are gases.

Properties of Metalloids Metalloids have properties of both metals and nonmetals. They are semiconductors at temperatures higher than room temperature. This means that they have a conductivity between that of a metal and that of a nonmetal, and can even change energy input and output by using electrical forces. They are all solids at STP.

Alkali Metals The alkali metals are found in group 1 (1A) of the periodic table. Valence electrons: 1 Oxidation Number: +1 They do not occur in nature as elements (in other words, they’re always in a compound). They form ionic compounds such as salts and oxides. They are also in bases. They are good conductors of heat and electricity, ductile, malleable, and soft enough to be cut with a knife. They have a silvery luster, low density, and low melting point. They are the most reactive metals.

Alkaline Earth Metals The alkaline earth metals are found in group 2 (2A) of the periodic table. Valence electrons: 2 Oxidation number: +2 Alkaline earth metals have similar characteristics to alkali metals, except that they are less reactive. They form salts, oxides, and bases.

Transition Metals The transition metals are found in groups 3 through 12. They have similar characteristics to the other metals except that: They are usually harder and more brittle than the metals in group 1 and 2. They often form colored compounds. (Think of the blue copper sulfate we’ve worked with.) Oxidation number: varies 3B 4B 5B 6B 7B 8B 1B 2B

Halogens The halogens are found in group 17 (7A) of the periodic table. Valence electrons: 7 Oxidation number: -1 They are all nonmetals and occur in combined form in nature. They exist in room temperature as gases (F 2 and Cl 2 ), a liquid (Br 2 ) and solids (I 2 and At). They are the most reactive nonmetals. Fluorine is the most reactive of all nonmetals (as anyone who has seen Breaking Bad discovered).

Noble Gases The noble gases are found in group 18 (8A) of the periodic table. Valence electrons: 8 Oxidation number: 0 They are colorless and odorless. They have very low boiling and freezing points. They rarely combine with other elements and are considered to be inert (nonreactive chemically). By Felix Burton (Flickr) [CC-BY-2.0]

Periodicity When the elements are arranged in order of increasing atomic number, there is a periodic reoccurrence of properties that leads to the group of elements in the periodic table. This periodic recurrence is known as periodicity. The position of the element in the periodic table can also be used to compare periodic trends in atomic radii, electronegativity, ionization energy, and ionic radii.

Nuclear Charge and the Shielding Effect All the periodic trends can be understood in terms of three basic rules. 1. SHIELDING EFFECT: Electrons tend to repel each other. 2. NUCLEAR CHARGE: Electrons want to get as close to the positively-charged nucleus as possible. (Opposites attract.) 3. OCTET RULE: Atoms want to have eight electrons in their outer shell, resembling a noble gas. Nuclear charge plays an important role in determining periodic trends. The shielding effect plays an important role in determining group trends.

Atomic Radii The atomic radius is half the distance between nuclei in two adjacent atoms. (Radius of an atom) Atomic radius increases moving down a group and decreases moving to the right across a period Decreases Increases Atomic Radii

Why? Shielding Effect: When you go down a group, more electrons are added, and these electrons repel each other. The atom gets bigger. Nuclear charge: When you go across a period, the electrons are more strongly attracted to the nucleus, and get smaller.

Ionization Energy Electrons are attracted to the nucleus of an atom, so it takes energy to remove an electron. The energy required to remove an electron from an atom is called the first ionization energy. Ionization energy decreases moving down a group and increases moving to the right across a period. In other words, the bigger the atom, the lower the ionization energy. Increases Decreases 1 st Ionization Energy

Why? Shielding effect: As you go down a group, the electrons increase and repel each other. The electrons are further away and easier to pluck out of an atom. This results in low ionization energy. Nuclear charge: As you go across a period, the electrons are closer together. It is thus harder to separate them. This results in high ionization energy.

Ionic Radii The ionic radius is the radius of a cation or anion. When the atom loses or gains electrons, the resulting ion changes in size from the original atom. Metals tend to lose electrons and form cations (positive ions). Nonmetals tend to gain electrons and form anions (negative ions).

Increases Atomic Radii & Ionic Radii Notice that since the metals are LOSING electrons, the other electrons can get closer to the nucleus, and SHRINK. (NUCLEAR CHARGE!) Since the nonmetals are GAINING electrons, the other electrons are now being repelled, and the ion will grow in size. (SHIELDING EFFECT!)

Electronegativity Electronegativity refers to the tendency for an atom to attract electrons to itself when it is chemically combined with another element. Electronegativity decreases moving down a group and increases moving to the right across a period Electronegativity Increases Decreases

Why? Shielding effect: As the electrons repel and spread out, they don’t want any more electrons. Thus the electronegativity is low. (ESPECIALLY IN METALS WHERE THEY ARE TRYING TO LOSE ELECTRONS!) Nuclear charge: As the electrons get closer, more can be added in. Thus, electronegativity is high. (ESPECIALLY IN NONMETALS WHEN THEY ARE TRYING TO GAIN ELECTRONS!)

Summary of Periodic Trends

Summary of Trends Electronegativity & Ionization Energy Increase Atomic Radii Increase Ionic Radii Increase Cation Radii Increase Anion Radii Increase