UNIT 6: The Periodic Table. CPChemistry GHS

Transcription

1 UNIT 6: The Periodic Table CPChemistry GHS

2 Objectives Explain organiza8on of periodic table in periods and groups. Iden8fy elements as belonging to representa8ve elements, transi8on elements, metals, nonmetals, or metalloids. Describe proper8es of metals, nonmetals, and metalloids. Describe proper8es of alkali metals, alkaline earth metals, halogens, and noble gases. Describe trends in metallic proper8es, atomic radius, ioniza8on energy, and electronega8vity through groups and periods in the periodic table. Explain periodic trends in terms of the rela8onship between subatomic par8cle aerac8on/repulsion and shielding effect.

3 What we already know Ma#er is anything that takes up space and has mass. All maeer is made of atoms Atoms are the building blocks But what is an atom?

4 Atomic Structure ~ The parts ~ An atom has 3 main parts Proton = posi8ve charge Neutron = no charge (neutral) Electron = nega8ve charge The nucleus (center) of the atoms is the loca8on for protons and neutrons. Electrons orbit around the nucleus (in a cloud)

5 Elements The elements, alone or in combina8ons, make up our bodies, our world, our sun, and in fact, the en8re universe

6 Periodic Table The periodic table organizes the elements in a par8cular way. One can gather infer informa8on about an element just from its posi8on in the period table! WHAT CAN YOU PREDICT? Physical properaes of elements Chemical reacavity of elements

7 Who was Mendeleev? In 1869, Dmitri Ivanovitch Mendeléev created the first accepted version of the periodic table He grouped elements according to their atomic mass He discovered that the groups (families) had similar chemical properaes Blank spaces were lez open to add new elements these hadn t been discovered or created yet, but he knew they would be! (SMART GUY!)

8 Who is Henry Mosley? Henry Mosley arranged the periodic table according to atomic number. This change established periodic law: the proper8es of the elements are periodic func8ons of their atomic number.

9 Valence electrons Outermost electrons in an atom The Periodic Table predicts how many electrons tend to be lost or gained for an atom Involved in chemical reac8ons (bonding)

10 Determining # of Valence Electrons Using the Periodic Table

11 OCTET RULE The OCTET RULE: Atoms tend to gain, lose, or share electrons un8l they are surrounded by 8 valence electrons. This is to achieve the same electron configura8on as the atom s closest noble gas on the periodic table for greatest stability! EXAMPLE: H 2 O shares electrons

12 Ions ~ Gaining or losing an electron In chemical reac8ons, atoms may gain or lose electrons IONS are elements that have gained or lost of one or more electrons resul8g in a net electric charge Loss of electron = net change of +1 for each electron Gain of electron = net change of -1 for each electron Posi8vely charged ions (Li+) are ca8ons Nega8vely charged ions (F-) are anions

13 Ions Loss of electron = net change of +1 for each electron Posi8vely charged ions (Al 3+ ) are caaons Gain of electron = net change of -1 for each electron Nega8vely charged ions (Cl - ) are anions

14 Predicting IONIC CHARGE Using the Periodic Table

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16 Properties of Metals Metals are good conductors of heat and electricity. Metals are shiny (high luster) Metals are ducale (can be stretched into thin wires) Metals are malleable (can be pounded into thin sheets) A chemical property of metal is its reac8on with water which results in corrosion

17 Properties of Non-Metals Non-metals are POOR conductors of heat and electricity Non-metals are NOT duc8le or malleable Solid non-metals are bri#le (break easily) They are dull (low luster!) Sulfur Many non-metals are GASES!

18 Properties of Metalloids Metalloids (metal-like) have some proper8es of BOTH metals and nonmetals They are SOLIDS that can be shiny OR dull They conduct heat and electricity beeer than non-metals but not as well as metals They are ducale and malleable Silicon

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21 GROUPS (Families) Periods Columns of elements are called groups or families. Each horizontal row of elements is called a period Elements in each group have similar but not iden%cal proper8es For example, lithium (Li), sodium (Na), potassium (K), and other members of group IA are all soz, white, shiny metals The elements in a period are not alike in proper8es The proper8es change greatly across a given row The FIRST element in a period is always an extremely ac8ve solid All elements in a group have the same number of valence electrons The LAST element in a period is always an inert gas * Inert = nonreac8ve

22 Hydrogen The hydrogen is located at top of group 1, but it is not a member of that family. Hydrogen is in a class of its own. Exists as a gas at room temperature. It has one proton and one electron in 1 st energy level Hydrogen only needs 2 electrons to complete its octet rule (fill its 1s orbital)

23 Alkali Metals The alkali metals are in the first column of the periodic table, Group 1. Atoms of the alkali metals have a single electron in their outermost level. They have 1 valence electron. Proper8es: shiny, have the consistency of clay, and are easily cut with a knife.

24 Alkali Metals They are the most reacave metals They react violently with water Alkali metals are never found as free elements in nature. They are always bonded with another element.

25 What does it mean for an element to be REACTIVE? We will be describing elements according to their reacavity Elements that are reac8ve bond easily with other elements to make compounds

26 What does it mean to be reactive? What makes an element reacave? Incomplete valence electron level All atoms (except hydrogen) want to have 8 electrons in their very outermost energy level (This is called the OCTET RULE) Atoms bond un8l this level is complete

27 Alkaline Earth Metals They are never found uncombined in nature. Shiny solids. They have two valence electrons. Very reac8ve (form ions with 2+ charge) Alkaline earth metals include magnesium and calcium, among others.

28 Transition Metals TransiAon Elements include those elements in the B families. Proper8es are similar to one another and to other metals, but their proper8es do not fit in with those of any other family. Metals you are probably most familiar: copper, 8n, zinc, iron, nickel, gold, and silver. Good conductors of heat and electricity.

29 Transition Metals The compounds of transi8on metals are usually brightly colored and are ozen used to color paints. Transi8on elements have 1 or 2 valence electrons, which they lose when they form bonds with other atoms. Many transi8on metals combine chemically with oxygen to form compounds called oxides Some transiaon elements can lose electrons in their next-to-outermost level.

30 Boron Family The Boron Family is named azer the first element in the family. 3 valence electrons. Tend to form ions with 3+ charge Includes a metalloid (boron), and the rest are metals. Includes the most abundant metal in the earth s crust (aluminum)

31 Carbon Family 4 valence electrons. This family includes a non-metal (carbon), metalloids, and metals. The element carbon is called the basis of life Tend to share electrons when they bond There is an en8re branch of chemistry devoted to carbon compounds called organic chemistry!

32 Nitrogen Family The nitrogen family is named azer the element that makes up 78% of our atmosphere. Includes non-metals, metalloids, and metals. 5 valence electrons. They tend to share electrons when they bond. Other elements in this family are phosphorus, arsenic, an8mony, and bismuth.

33 Oxygen Family 6 valence electrons. Most elements in this family share electrons when forming compounds. Oxygen is the most abundant element in the earth s crust. Extremely ac8ve and combines with almost all elements.

34 Halogen Family The elements in this family are fluorine, chlorine, bromine, iodine, and asta8ne. 7 valence electrons. MOST REACTIVE non-metals. Halogen atoms only need to gain 1 electron to fill their outermost energy level. They react with alkali metals to form salts. They are never found free in nature.

35 Noble Gases Colorless gases that are extremely unreacave. Running electricity through produces color. Inac8ve because their outermost energy level is full. (Most stable configura8on.) Do not readily combine with other elements to form compounds = inert The family of noble gases includes helium, neon, argon, krypton, xenon, and radon. All the noble gases are found in small amounts in the earth's atmosphere.

36 Rare Earth Elements (inner transition metals) The thirty rare earth elements are composed of the lanthanide and ac8nide series. Most elements in the ac8nide series are called trans-uranium, which means synthe8c or manmade. Called the seeds of technology

37 What is a TREND? A TREND is a predictable change in a par8cular direc8on. Periodic TRENDS allow for predic8ons to be made about chemical behavior. Periodic TRENDS can be related to atomic structure and electron configuraaon.

38 Diatomic Molecules Some elements only exist in nature as diatomic molecules: 2 atoms of the same element bonded together. Generates stability by sharing electrons to fill energy highest level.

39 What is PERIODICITY? Trends are recurring in elemental proper8es. PaEerns can be deduced by relaang electron configuraaon for elements meaning, moving across a period and down a group in the periodic table. Chemical behavior is related to ELECTRONS. Periodic trends allow predic8ons to be made about chemical behavior. Described in generality there ARE SOME EXCEPTIONS!

40 KEY POINTS to remember! like aeracts unlike protons (+) a#ract electrons (-) like repels like electrons (-) repel electrons (-)

41 KEY POINTS to remember! SHIELDING EFFECT When an atom has more than one shell, there is a DECREASE in aerac8on between the valence electrons and the nucleus

42 Shielding Effect - EXAMPLE Hydrogen has electrons in ONLY 1 SHELL NO SHIELDING Lithium has electrons in 2 SHELLS Inner electrons shield the nucleus, offserng some of the protons aerac8on to the electrons

43 Atomic Radius Atomic radius = size of an atom Ionic radius = size of an ion Actual atomic radius is difficult to determine. Best representa8on is the distance between the nucleus and the outermost electron shell (valence shell). Determined by taking ½ distance between two nuclei of covalently bonded atoms.

44 Atomic Radius PERIODIC TREND Atomic radius in pm

45 Atomic Radius vs. Atomic Number As atomic number increases across a period, the atomic radius decreases. As principle energy level increases going down a group, the atomic radius increases.

46 Atomic Radius What s happening? TWO FACTORS: Nuclear charge (how many protons are present) Shielding effect of electrons in inner shells

47 Atomic Radius What s happening? More protons are added moving across a period (atomic number increases) Filling electrons in SAME principle energy level STRONGER PULL on electrons ATOMIC RADIUS DECREASES!

48 Atomic Radius What s Happening? Moving down a group, principle energy level increases. More orbitals are added Electrons in outer orbitals experience shielding effect Electrons are not pulled in as 8ghtly toward the nucleus

49 Atomic Radius: Compare groups and periods

50 IONIZATION ENERGY Periodic Trend IonizaAon energy is the amount of energy required to remove a valence electron from the outermost shell in an atom. Losing electrons forms posi8vely charged ions called caaons. IE is also affected by number of protons present in nucleus and by electron shielding. Energy must be put in to remove electrons.

51 IONIZATION ENERGY - TREND

52 1 st IONIZATION ENERGY Energy required to remove the 1 st valence electron

53 Ionization Energy What s happening? Moving across a period, number of protons increases, so posi8ve charge increases (GREATER aerac8on to electrons!). SAME principle energy level, so NO addi8onal electron shielding Electrons are HELD MORE STRONGLY and require MORE ENERGY to remove

54 Ionization Energy What s happening? Moving down a group, number of protons increases, so posi8ve charge increases (GREATER aerac8on to electrons!). BUT addi8onal energy levels AND addi8onal electron shielding Electrons are HELD LESS STRONGLY and require LESS ENERGY to remove

55 Degrees of IONIZATION ENERGY Some8mes, more than one electron will be removed from an atom. Each successive electron that is removed is progressively more difficult to remove, requiring more and more energy WHY? Fewer electrons à less repulsion Fewer electrons à closer to nucleus causing stronger aerac8on to protons

56 Successive Ionization Energies

57 Electron Affinity Periodic Trend Electron affinity is the change in energy, measured in kj/mol, for a neutral atom when gaining an electron; the rela8ve likelihood for gaining an electron. Energy may be added or released Gaining an electron forms a nega8vely charged ion called an anion.

58 Electron affinity Periodic Trend TWO FACTORS: Affected by atomic structure (number of protons; energy levels/orbitals). Affected by how many electrons needed to fulfill octet rule for valence electrons (achieve an electron configura8on same as its closest noble gas)

59 Electron Affinity Periodic Trend

60 Electron Affinity What s happening? Moving across a period for main group elements, the closer the element is to the noble gas configura8on, such as elements in groups 15-17, the higher the electron affinity. Moving across a period, atomic radius decreases, so pull from protons is greater.

61 Electron Affinity What s happening Moving down a group on the periodic table, energy levels increase and atomic radius increases, causing less pull on electrons from the nucleus

62 Electronegativity Periodic Trend ElectronegaAvity measures the tendency of an atom to aeract a bonding pair of electrons. The atom with GREATER electronega8vity will aeract the electrons more strongly Creates polarity Difference in electronegaavity is 0.9

63 Electronegativity Periodic Trend Measured with Pauling Scale Electronega8vity increases across a period Electronega8vity decreases down a group

64 Periodic Trends: ALL TOGETHER How do you remember the trends? Atomic radius is the ONLY trend that has a different paeern: