Unit 5 ● What Atoms Look Like Properties & Trends

Classifying the Elements We can classify the elements in two different ways.

Two ways to classify elements Elements can be classified into metals, nonmetals, and semimetals. Elements can also be classified into groups or families. You should be able to do both. Semimetals

Properties of Metals Metals are good conductors of heat and electricity. They are shiny and lustrous. Metals can be pounded into thin sheets (malleable) and drawn into wires (ductile). Metals do not hold onto their valence electrons very well. They have low electronegativity.

Properties of Nonmetals Nonmetals are poor conductors of heat and electricity. Exception: graphite is a good conductor. Nonmetals are brittle. If you hit them with a hammer, they shatter and turn to powder. Good examples of nonmetals are sulfur, carbon, and all the gases.

More on Nonmetals The seven diatomic molecules are all nonmetals. Remember that hydrogen is a nonmetal even though it is located on the left side of the table with the metals. Nonmetals strongly attract their electrons. They have high electronegativity values and therefore form negative ions.

Semimetals Si These elements have properties that are in- between those of the metals and nonmetals. They are very important for making transistors and computer chips. Silicon (Si), germanium (Ge), and tellurium (Te) are shown. Different books include polonium (Po) and leave out astatine (At). Te Ge

Semimetals are also called metalloids.

Families of the Periodic Table Five important chemical families.

2Na + 2H2O  H2 + 2NaOH Alkali Metals This family is found in column 1 of the periodic table. The all form 1+ ions. They react rapidly with water (H2O) and form flammable H2 gas. Their chemistry involves losing their one valence electron.

Alkali Metals They are soft metals and can be cut with a knife. They are stored under oil or sometimes inside sealed glass tubes. Allaki metals have characteristic flame test colors: Sodium is orange. Potassium is violet.

Alkaline Earth Metals These elements always from 2+ ions in their compounds and react slowly with H2O. Their chemistry involves losing their two valence electrons. We use magnesium (Mg) in one of our labs to form hydrogen gas. Calcium is important for bones and teeth. The loss of it is osteoporosis. Ca + 2H2O  H2 + Ca(OH)2

Xe The Noble Gases He Helium was first found in the Sun. “Neon lights” with a red- orange glow contain neon gas. Argon is the 3rd most abundant gas in the air. Xenon is used in flashes and bright headlights. Radioactive radon can collect in the basement. He Xe

Halogens These elements always form 1- ions. They each have 7 valence electrons. Halogens react with metals to form salts. Halo-gen = “salt former”. 2Na + Cl2  2 NaCl Halogens gain an electron to fill their outer shell. This family has gases, a liquid, & a solid element.

More on Halogens All of the halogens are diatomic. Halogen bulbs are very bright, but very hot. Halogens are very electronegative (they strongly attract electrons). Fluorine is the most (4.0). They gain electrons (are reduced) and act as good oxidizers. Chlorine (Cl2) is used to purify water.

Hydrogen— an alkali metal? Hydrogen has properties like the alkali metals & like the halogens. It forms 1+ ions. It combines with halogens. It loses its 1 valence electron. It is located with the alkali metal family. H2 + Cl2  2 HCl

Li+ & H- Hydrogen – a halogen? Lithium hydride: It has one less electron than a noble gas (He). It can combine with alkali metals. 2Li + H2  2LiH In this case, H gains 1 electron (forms H- ion). Hydride has a 1- ion. Hydrogen is diatomic like all of the other members of the halogen family. Lithium hydride: Li+ & H-

Trends in the Periodic Table Trends in size, ionization energy, and electronegativity. The trend in size is key.

Trend in Size You should be able to state what happens to the size of an atom as you move across the periodic table and down the periodic table. You should also be able to state a reason for these trends. Periods are horizontal rows. Groups or families are vertical columns.

Trends in Size The size of an atom is due to the size of the electron cloud. There are repulsions between the electrons and electrons. (Like charges repel.) There are attractions between the electrons and protons. (Opposite charges attract.)

Trends in Size  More protons  More layers Across: The atoms get smaller because there are more protons pulling in the layer of electrons. Down: The atoms get larger because there are more layers of electrons. Each layer is farther from the nucleus.  More protons  More layers

Ionization Energy This is the energy needed to remove an electron. It is easier to remove an electron from a larger atom because the electron is farther from the nucleus and feels less attraction.

Sizes of Ions Each time and electron is removed, the ion becomes smaller because there is less repulsion between the electrons. Each successive electron removed has a higher ionization energy. Atoms that gain electrons become larger. There is a BIG jump in “IE” when the valence electrons are removed.