Chemistry Chapter 6 The Periodic Table and Periodic

Chemistry Chapter 6 The Periodic Table and Periodic Law

6. 1 Development of the Modern Periodic Table § Objectives: § 1. Explain how elements are organized in a periodic table § 2. Identify key features of the periodic table

How the Elements are Organized + Early & Modern § Chemists used the properties of elements to sort them into groups § Dimitri Mendeleev was the first to arrange the elements in the periodic table in order of increasing mass § In the modern periodic table, elements are arranged in order of increasing atomic number § http: //www. inorganicventures. com/extra s/pertable/

§ The pattern of properties within a period repeats as you move from one period to the next § Elements that have similar properties end up in the same column in the table § PERIODIC LAW: when elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties § Q: How many periods are there in a periodic table? § A: 7

Key Features: 3 Broad Classes § Groups with letter A are called representative elements § Table has three categories: metals, non-metals, and metalloids § Metals to the left, non-metals to the right, and metalloids along the stair step § Metalloids are also called semiconductors

§ Metals have: § High conductivity § High luster (when clean) § Are ductile-drawn into wires § Are malleable § Non-metals: § Poor conductors § nonlustrous

§ Metalloids (border the stairstep) generally have some properties of metals and some properties of nonmetals § Here’s a preview of the table: § 1 A metal elements known as alkali metals § 2 A metal elements known as alkaline earth metals § 7 A nonmetal elements known as halogens (halogens means “salt formers” § 0 nonmetal elements known as noble gases (also called group 8 A)

§ On the flat of part of the table between groups 3 – 12 lie the group B elements § These are the transition elements which are divided into transition metals and inner transition metals § The inner transition metals are further divided into the lanthanide series and actinide series § The inner transition metals are sometimes called the rare earth metals

6. 2 Classification of the Elements § Objectives: § 1. Explain why elements in the same group have similar properties § 2. Identify the four blocks of the periodic table based on their electron configuration

Classifying by Electron Configuration § Elements can be sorted in noble gases, representative elements, transition metals or inner transition metals based on their electron configurations § Electrons exist in “shells” (similar to orbits) around the nucleus

§ The first shell can hold up to 2 electrons § The second shell can hold up to 8 electrons & the third up to 18 e- (count the number of elements across the period) § If the shells are full, the atom is especially stable § All elements in Group 8 A, also called the 0 elements, have full outer shells § These are the noble gases and they are inert & nonreactive with other elements because of their full shells § The elements in the 8 A group have a charge of 0

§ Elements on the table are neutral, but the groups have tendencies § All elements in group 1 A, the alkali metals, readily lose one electron to complete their outer shell § If they lose that one electron, the 1 A element will carry a charge of 1+ § Group 2 A, the alkaline earth metals, readily loses 2 electrons § Group 2 A will carry a charge of 2+ § Group 3 A will carry a charge of 3+ if it loses 3 electrons

§ Group 4 A has 2 possible charges: 4+ or 4 - because it can either lose or gain 4 electrons to complete its outer shell § Group 5 A also has 2 possible charges: 5+ or 3§ Group 6 A carries a 2 - charge because it gains 2 electrons to complete its outer shell § 7 A (the halogens) has a 1 - charge § 8 A (the nobles) has a 0 charge because its outer shell is already full § The representative elements are located in the elevated part of the table and are group A

§ The transition metals, on the flat part of the table, are the B elements § Two main groups: transition metals and inner transition metals § Inner transition metals also known as the rare-earth elements § Many elements in the transition group can have variable charges

§ There are some general, more common charges these elements have § Most elements in this group have a charge of 2+ except for the groups beginning with chromium (Cr, 6 B) and copper (Cu, 1 B) § Elements in the Cr and Cu groups generally have a 1+ charge § 80% of elements are metals, almost all solid at room temperature

§ Metals are located downstairs to the left on the table § Metalloids are located on either side of the stairs § Nonmetals are about 20% of the elements & are located upstairs to the right with the exception of hydrogen § General rules: § 1. positive elements react with negative elements § 2. elements with full outer shells do not react

The Four Blocks § The four blocks are called s, p, d and f § This explains the odd shape of the periodic table § Each block represents an atom’s energy sublevel being filled with valence electrons § S level holds up to 2 e- (one orbital) § P level holds up to 6 e- (three orbitals) § D level holds up to 10 e- (five orbitals) § F level can hold up to 14 e- (seven orbitals)

6. 3 Periodic Trends § Objectives: § 1. Compare period and group trends of several properties § 2. Relate period and group trends in atomic radii to electron configuration

Trend in Atomic Size § Size is expressed as atomic radius § Definition: atomic radius is one half the distance between the nuclei of two atoms of the same element when the atoms are joined § In general, atomic size increases from top to bottom within a group and decreases from left to right across a period

Trend in Ions § Definition: an ion is an atom or group of atoms that has a positive or negative charge due to loss or gain of an electron § An atom is electrically neutral due to equal numbers of electrons and protons § Electrically neutral atoms are different from stable atoms § Stable atoms have full outer electron shells § Atoms strive to have the stable configuration of the nobles

§ Positive and negative ions form when electrons are transferred between atoms § The transfer occurs in way that the charge will add up to zero § Definition: a cation is an ion with a positive charge § Definition: an anion is an ion with a negative charge § Ionic radius from left to right across the period for positive ions gradually decreases § Beginning about group 5 A or 6 A the size of the much larger anions gradually decreases

Ionization Energy, Size & Trends § Definition: the energy required to remove an electron from an atom is the ionization energy § This energy is measured when the atom is in a gaseous state § Definition: the energy required to remove the first electron is the first ionization energy

§ First ionization energies tend to decrease from top to bottom within a group and increase from left to right across a period § SIZEWISE: Cations are always smaller than the atoms from which they formed (because they lost one or more electrons) § SIZEWISE: Anions are always larger than the atoms from which they form (because they gained one or more electrons)

Trend in Electronegativity § Definition: electronegativity is the ability of an atom of an element to attract electrons when the atom is in a compound § In general, nobles don’t attract electrons or form many compounds § Electronegativity is small to zero for nobles § The most electronegative element is fluorine

§ Electronegativity generally decreases as you move down a group and increases from left to right across a period § For representative elements, the values tend to increase from left to right across a period § The trends that exist among these properties can be explained by variations in atomic structure