GROUPS/Families & VALENCE ELECTRONS

GROUPS/Families & VALENCE ELECTRONS CHAPTER 5.3

Elements in a groupor “family” have similar properties. Elements in a period have the same number of electron shells or energy levels.

Valence electrons • Why do the elements in a group have similar properties?

Valence electrons • Why do the elements in a group have similar properties? • They have the same number of valence electrons. • The properties are not identical because the valence electrons are in different energy levels. • A valence electron is an electron that is in the highest occupied energy level of an atom. • Outer most electron shell

Electrons Filling shells as atomic # increases (# of electrons goes up as # of protons goes up): B Li Be H He Na C N Ne 1st shell now full, start 2nd 5 3 1 2 4 Atomic # 1 2 3 Valence e’s 1 2 e- capacity: 1st shell = 2 2nd shell = 8 3rd shell = 8 4th shell = 18 5th shell = 18 6th shell = 32 7th shell = 32 6 7  Atomic # 2nd shell now full, start 3rd 10 4 11 Valence e’s 5 8 1

Valence electrons • How do we determine the number of valence electrons? • When groups in the periodic table are labeled as Series A and Series B: • For Series A (Groups 1A - 8A): • group number = the number of valence electrons for an element in that group. • Valence electrons play a key role in chemical reactions. • Properties vary across a period because the number of valence electrons increases from left to right.

Octet Rule • Atoms are most stable if their outer most electron shell is filledor empty. • Filled shell contains 8 electrons (octet) • Except for H and He (atomic #1 & #2) • Atoms gain, lose, or share valence electrons in order to fill or empty their outer shell • Atoms gain, lose, or share electrons based on what is easiest.

Na Octet Rule • Na has 11 protons and 11 electrons. • Period 3 = 3 e- shells • Group 1A = 1 Valance e- • 2 e- in 1st shell (full) • 8 e- in 2nd shell (full) • 1 e- in 3rd shell (valence) proton charge (11 x +1) = +11 + electron charge (11 x -1) = -11 net charge = 0 (neutral)

Octet rule • When atoms lose or gain valence electrons  no longer neutral • Na has 1 valence e- -- easier to lose 1 than gain 7 to fulfill octet rule • leaves only 10 electrons • (2 e- in 1st shell; 8 e- in 2nd shell; 1 e- in 3rd shell)  (11 x +1) • (2 e- in 1st shell; 8 e- in 2nd shell; no e- in 3rd shell)+ (10 x -1) = 1+ • Example: Cl has 7 valence e--- easier to gain 1 than lose 7 • (2 e- in 1st shell; 8 e- in 2nd shell; 7 e- in 3rd shell) (17 x +1) • (2 e- in 1st shell; 8 e- in 2nd shell; 8 e- in 3rd shell)+ (18 x -1) = 1-

Properties Groups/Families

Group 1A – Alkali Metals • 1 Valence Electron. • Soft & Silvery • Extremely Reactive (Most reactive Metals) • Found in nature only in compounds. • NOT found free in nature • Mix well with water • The reactivity of alkali metals increases from the top of Group 1A to the bottom.

Group 1A – Alkali Metals Unlike most metals Sodium is soft enough to cut with a knife. Sodium reacts violently with water and releases enough energy to ignite the hydrogen gas that is produced.

Group 1A – Alkali Metals • Potassium (& Sodium) • Stored under oil to keep them from reacting with the oxygen and water vapor in air. • Cesium • So reactive that it is usually stored in a sealed glass tube containing argon gas. • Why argon?

Group 2A – Alkaline Earth Metals • 2 Valence Electrons • Similar to Alkali Metals • Harder than metals in Group 1A • Higher melting points • The melting point of magnesium is 650°C; sodium 98°C • Almost as reactive as Alkali metals • NOT found free in nature • Reactivity increases • From top to bottom

Group 2A – Alkaline Earth Metals • Differences in reactivity among the alkaline earth metals are shown by the ways they react with water. • No reaction occurs when beryllium is added to water. • Magnesium will react with hot water but not cold water. • Calcium, strontium, and barium react easily with cold water.

Magnesium • Photosynthesis: Chlorophyll • Creates alloys stronger yet lighter than steel • Calcium • Oyster shell and a pearl - calcium carbonate (Ca, C, & O). • Also found in toothpaste • Plaster cast - calcium sulfate. Oyster shell with pearl Spinach plant

Group 3A – The boron family • 3 Valence Electrons • Most are metals • Well-known metal – Al (aluminum) • Less familiar metals - Ga (gallium), In (indium), and Tl (thallium). • Boron is a metalloid

Group 3A – The boron family • Aluminum • Most abundant metal in Earth’s crust. • Less reactive than Na and Mg • Strong, lightweight, and malleable. • Good conductor of electric current. • Boron • B, Si, & O form a compound used to make glass that does not shatter due to rapid temperature change. • laboratory glassware • cookware that can go directly from the oven to the refrigerator.

Group 4A – The carbon family • 4 Valence electrons • Family Contains • 1 Nonmetal - C (carbon) • 2 metalloids - Si (silicon) & Ge (germanium) • 2 metals - Sn (Tin) & Pb(Lead) • Notice that the metallic nature of the elements increases from top to bottom within the group. Germanium is a better conductor of electric current than silicon.

Group 4A – The carbon family • Carbon • Except for water, most of the compounds in your body contain carbon. • Life on Earth would not exist without carbon. • Reactions that occur in the cells of your body are controlled by carbon compounds • Silicon • 2ndmost abundant element in Earth’s crust. • The clay used to produce pottery contains silicon compounds called silicates.

Group 5A – The Nitrogen family • 5 Valence electrons • Can share electrons to form compounds • Family Contains: • 2 nonmetals - N (nitrogen) & P (phosphorus) • 2 metalloids - As (arsenic) & Sb (antimony) • 1 metal - Bi (bismuth). • Group 5A includes elements with a wide range of physical properties. • Nitrogen is a gas • Phosphorus is a solid nonmetal • Bismuth is a dense metal.

Group 5A – The Nitrogen family • When air is cooled- O condenses before the N due to its lower boiling point • Much of the Nobtained from air is used to produce fertilizers. • The numbers on the bags of fertilizer are, from left to right, the relative amounts of nitrogen, phosphorus, and potassium.

Group 6A – The Oxygen family • 6 Valence electrons • Family Contains: • 3 nonmetals - O (oxygen), S (sulfur), & Se (selenium) • 2 metalloids - Te (tellurium) & Po (polonium) • Reactive

Group 6A – The Oxygen family • Oxygen • Most abundant element in Earth’s crust. • Complex life forms need O to stay alive because O is used to release the energy stored in food. • Ozone (O3) is another form of the element oxygen. • Sulfur • One of the first elements to be discovered because it is found in large natural deposits.

Group 7A – Halogens • 7 Valence electrons • All Nonmetals • At room temperature: • chlorine is a gas, • bromine is a liquid • iodine is a solid. • MOST Reactive of the nonmetals • Often find these elements bonded with elements from Group 1A

Group 7A – Halogens • Despite their physical differences, the halogens have similar chemical properties. • React easily with most metals. • Image: • Chlorine reacting with steel wool 

Group 8A – the noble gases • 8 Valence electrons = Full Shell – Octet Rule • Helium (He) has only 2 valence electrons = Full • All Non-metals • Extremely Unreactive • Colorless and odorless

Group 8A – the noble gases • When electric current passes through noble gases, they emit different colors. • He (Helium) emits pink, • Ne (Neon) emits orange-red, • Ar (Argon) emits lavender, • Kr (Krypton) emits white • Xe (Xenon) emits blue.

Assessment question • Why do elements in a group have similar chemical properties? • They have the same number of valence electrons. • They have the same ratio of protons to neutrons. • Their atomic masses are multiples of the least massive element of the group. • They have the same number of total electrons.

Assessment question • Which Group 2A element would you expect to react most readily with water? • beryllium (Be) • calcium (Ca) • barium (Ba) • radium (Ra)

Assessment question 3. In general, the metallic characteristics of within a period decreases from left to right. • True • False

Assessment question 4. Elements of the Nitrogen Family have a. 4 Valence electrons b. 6 Valence electrons c. 5 Valence electrons d. 7 Valence electrons

Assessment question 5. Atoms are most stable if their outer most electron shell is filled or empty. a. True b. False

Assessment question 5. Atoms are least stable if their outer most electron shell is filled or empty. a. True b. False

GROUPS/Families & VALENCE ELECTRONS