Electrons and Periodicity

Wow, that periodic table is useful.Electrons and PeriodicityArrangement of the Modern Periodic TableIn 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 118 or 18 with A/B notationTall columns are notated as A Main group elementsShort columns are notated as BNumbering Groups

1A 2A3A 4A 5A 6A 7A 8A3B 4B 5B 6B 7B 8B 1B 2B Main Group ElementsGroups are numbered either one through eighteen or one through eight with an A notation given to the tall columns and B notation to the short columns. Group A elements are known as the main group elements. Main group elements tend to show periodic patterns most clearly and consistently.3Step-wise line that begins at the element boron and moves downward in a zigzag pattern divides the tableMetals are to the left of the line Nonmetals are to the right of the lineAlong the line are the metalloidsPossess properties of both metals and nonmetals

Metals, Nonmetals, and Metalloids

MetalloidsThe periodic table may be divided into a left half and right half using a step-wise line that begins at the element boron and moves downward in a zigzag pattern. To the left of the line are the metals and to right are nonmetals. Along the line are the semi-metals or metalloids, shown in blue in the image, which possess properties of both metals and nonmetals. 5Properties of MetalsThey are malleable, ductile, and have luster.They are good conductors of heat and electricity.They have relatively high densities. They are solids at standard temperature and pressure (STP), except for mercury, which is a liquid.Properties of NonmetalsThey are dull and brittle.They dont 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 MetalloidsMetalloids 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 MetalsThe alkali metals are found in group 1 (1A) of the periodic table. Valence electrons: 1Oxidation Number: +1They do not occur in nature as elements (in other words, theyre 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 MetalsThe alkaline earth metals are found in group 2 (2A) of the periodic table.Valence electrons: 2Oxidation number: +2Alkaline earth metals have similar characteristics to alkali metals, except that they are less reactive. They form salts, oxides, and bases.

Transition MetalsThe 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 weve worked with.)Oxidation number: varies

3B 4B 5B 6B 7B 8B 1B 2B 3 4 5 6 7 8 9 10 11 12HalogensThe halogens are found in group 17 (7A) of the periodic table.Valence electrons: 7Oxidation number: -1 They are all nonmetals and occur in combined form in nature. They exist in room temperature as gases (F2 and Cl2), a liquid (Br2) and solids (I2 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 GasesThe noble gases are found in group 18 (8A) of the periodic table. Valence electrons: 8Oxidation number: 0They 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]

PeriodicityWhen 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 EffectAll the periodic trends can be understood in terms of three basic rules.SHIELDING EFFECT: Electrons tend to repel each other.NUCLEAR CHARGE: Electrons want to get as close to the positively-charged nucleus as possible. (Opposites attract.)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 RadiiThe 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

DecreasesIncreasesAtomic RadiiWhy?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 EnergyElectrons 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.

IncreasesDecreases1st Ionization EnergyWhy?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 RadiiThe 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).

IncreasesAtomic Radii & Ionic RadiiNotice 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!)ElectronegativityElectronegativity 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

ElectronegativityIncreasesDecreasesWhy?Shielding effect: As the electrons repel and spread out, they dont 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 IncreaseAtomic Radii IncreaseIonic Radii IncreaseCation Radii IncreaseAnion Radii IncreaseThe trend for atomic radius is the most important to remember since all the other trends can be determined by looking at the atomic radius. The atomic radius increases towards the bottom left corner of the periodic table. Remember that like atomic radius, ionic radius increases as you move down a group. As you move the left across a period, the radii of cations will increase and the radii of anions will increase.The trends for electronegativity and ionization energy are opposite the trend for radius so the elements with the largest electronegativities and ionization energies will be at the top right corner of the periodic table. Remember however, that noble gases are not typically included in the electronegativity trend since they do not usually form bonds. Therefore, fluorine is the most electronegative element, while helium has the highest ionization energy value.

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