Chapter: Atomic Structure and Chemical Bonds

Transcription

1 Table of Contents Chapter: Atomic Structure and Chemical Bonds Section 1: Why do atoms combine? Section 2: How Elements Bond

2 Table of Contents Chapter: Atomic Structure and Chemical Bonds Section 1: Why do atoms combine? ***Atoms combine in different arrangements to form all the substances we know. **Atoms combine to have a stable electron arrangement.

3 What you will learn: How electrons are arranged in an atom That the electron arrangement is important to the properties of this atom and to the capability of reacting with other atoms. This information will help us understand chemical reactions

4 1)The nucleus: represents most of the mass 2) The electron cloud with electrons that are very small and mostly empty space 3) Nucleus very small compared to the electron cloud. The atom has:

5 Atoms Charges Nucleus has (+) charge = protons Electrons have a (-) charge and move randomly in the electron cloud

6 What is Element Structure or Element Configuration? ** Element Structure is the specific number of protons, neutrons, and electrons in an atom and how the electrons are distributed in the electron cloud Element Structure will determine the chemical and physical properties of the atoms and how atoms react with other atoms.

7 Electron Arrangement The electron cloud has several energy levels. Electrons will move from one energy level to another. Each level has a different amount of energy

8 Energy levels ( shells)

9 Energy Levels Electrons are attracted by the nucleus - so USUALLY the electrons will occupy the energy levels closer to the nucleus first.

10 Number of electrons Each energy level can hold a different number of electrons ( 2, 8, 18 ) some exceptions

11 **The electrons in the outermost energy level always have the greatest energy and are less stable. **Less stable = will react easily with other atoms. **The force that attracts them to the nucleus is much weaker because it is an area far from the protons.

12 ***The electrons that occupy the last energy level are called valence electrons and are the electrons involved in chemical reactions Notetaking wkst A,B and C

13 Energy Levels 2n 2 formula used to calculate the maximum number of electrons an energy level can hold n = the number of the energy level.

14 Electron Configurations ** Octet Rule states that: An atom with 8 electrons on the last energy level is considered stable. There are exceptions Helium and Hydrogen need 2 ( one energy level only page 467 fig 5) *Usually, if the last energy level is complete, the atom is stable

15 Valence Electrons in the Periodic table Groups handout Elements in Group 1: 1 valence electron (Hydrogen) Group 2: 2 valence electrons Group 13: 3 valence electrons Group 14: 4 valence electrons Group 15: 5 valence electrons Group 16: 6 valence electrons Group 17: 7 valence electrons Group 18: 8 valence electrons except for helium, which has 2 (these are all stable) Groups 3-12 changes

16 Atoms will react with other atoms to become stable, forming molecules. A chemical bond is the force that holds two atoms together. **3 ways an atom can combine with others and became stable: An atom can gain, donate, or share electrons.

17 -Atoms with 1, 2 or 3 electrons in the outer energy level will lose electrons to become stable -Atoms with 5, 6 and 7 electrons in the outer energy level, will receive electrons to become stable - Atoms with 4 usually share electrons

18 Representing Atomic Configuration or Structure There are 2 ways we can represent the electron configuration of atoms: Lewis Structure seen on page 467 also called Electron Dot Diagram Bohr Model of the atom

19 **This representation of the atom is called Bohr Model, shows the distribution of all the electrons of an atom How to do the Bohr Model Ex: Oxygen -Atomic number -Number of electrons -Distribute the electrons -Which group to check Draw the Bohr model for Sodium - Na

20 Sodium Let s do the Bohr Model for Phosphorus, Fluorine and Hydrogen

21 Phosphorus atomic number - 15

22 Fluorine Atomic number - 9

23 Hydrogen atomic number = 1 one electron in the last shell, very reactive

24 Lewis Structure or Electron Dot Diagram Bohr Model of the atom

25 Electron dot diagram will show how the electrons are distributed in the last energy level. They are useful to represent chemical reactions among atoms. Let s do it for NEON

26 Find the group the atom belongs to in the PT Refer to your Number of Valence Electrons per group handout you will know the number of valence electrons in that atom The dots are written in pairs on four sides of the element symbol. Start by writing one dot on the top of the element symbol, then work your way around adding dots to the right, bottom, and left.

27 Valence Electrons Group 1: 1 valence electron Group 2: 2 valence electrons Group 3: 3 valence electrons Group 13: 3 valence electrons Group 14: 4 valence electrons Group 15: 5 valence electrons Group 16: 6 valence electrons Group 17: 7 valence electrons Group 18: 8 valence electrons except for helium, which has 2

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29 CHAPTER 16 - SECTION 2 How elements bond: Chemical bond is the force that keeps two atoms together. We said that: Atoms can gain, donate or share electrons

30 There are 3 types of bonds Ionic Bonds *** Covalent Bonds **** Metallic Bonds

31 In Ionic Bonds: one atom gives an electron, the other receives

32 In Covalent Bonds: atoms will share electrons

33 **Bonds Atoms form bonds with other atoms using the electrons in their outer energy level. Atoms form bonds so both atoms will have an stable atomic structure Atomic Stable Structure means that the outer energy level of that atom is complete or has 8 electrons.

34 **IMPORTANT TO REMEMBER Ionic bonds metals and non metals ( also metalloids) Covalent between non metals (also metalloids) Metallic between metals

35 Ionic Bonds Loss and Gain Sodium has only one electron in its outer energy level. Removing this electron empties this level and leaves the level below complete, and the atom is stable

36 Ionic Bonds Loss and Gain By removing one electron, sodium becomes stable and becomes a positive ion : Na+ ( lost one negative charge - not neutral anymore)

37 Ions Formation Na + and Cl - Sodium becomes a + ion because it gives one electron Chlorine becomes a ion because it receives one electron Na and Cl combine forming NaCl This is an Ionic Bond

38 Chemical Reaction representation: Electron Dot Diagram Ionic Bond and NaCl is an ionic compound.

39 More Gains and Losses Can elements lose or gain more than one electron? EX: Magnesium and Oxygen 1) Which Groups in the PT, this atoms belong to? 2) How many electrons do they have in the outer energy level? 3) Which one will lose and which one will gain?

40 More Gains and Losses Can elements lose or gain more than one electron? Mg can loose 2 and Oxygen can gain 2 electrons to became stable. When this happens, magnesium oxide (MgO) is formed and is an ionic compound

41 Practice: Ionic bonds

42 Show the transfer of electrons in the following combinations Na + Cl Cl + Ca K + F Mg + I Al + Br Mg + Br Ca + O K + O Be + S Na + O Fe + O ( Fe has 2 valence electrons) Cu + Cl ( you will have to do the Bohr Diagram of Cu to find out the number of valence electrons)

43 Fe has 2 valence electrons The reason why the 3 rd energy level has 14 and not 18 involves principles of quantum mechanics.

44 Symbols for Compounds Elements are represented by symbols = letters molecules are represented by symbols and numbers. Ex: H 2 O 2 atoms of Hydrogen and one of water The number 2 is called a subscript H 2 O is called a chemical formula (for water)

45 Chemical Formulas Importance of the subscript CO carbon monoxide / CO 2 carbon dioxide Water H 2 O / Hydrogen Peroxide - H 2 O 2

46 Covalent Bonds electron sharing because of the number of electrons in their outer levels, some atoms will share electrons Bonds between nonmetals

47 The Covalent Bond Covalent bond atoms share the electrons in the last energy level During covalent bonding a molecule or a molecular compound is formed

48 3 types of Covalent bonds: single, double and triple

49 6 and 4 atoms are too many to donate so atoms will share

50 Double Bond CO2

51 Triple Bond N has 5 e- in the last energy level

52 Practice: Covalent bonding

53 Show how the pairs of atoms below share electrons. They can share 1,2 or 3 electrons in order to become stable 1)H+H 6)F+F 2)O+O 7)N+N (N 2 ) 3)C+O (CO 2 ) 8)H+O (H 2 O) 4)N+O (N 2 O 2 ) 9)S + O 5)H+F 10)N + H (NH 3 )

54 Metallic Bonding Metals share electrons in a special way. Electrons are not bonded to any particular atom. They are free to move from one atom to another creating a sea of electrons or a shared pool of electrons.

55 Metallic Bonding is responsible for many of the metals properties such as: being good conductors of electricity and being malleable. Metals share electrons in a special way. Electrons are not bonded to any particular atom.

56 According to what you know about the different groups in the periodic table: -Which Groups of atoms will donate electrons? Which Groups will receive electrons??? You can use the valence electrons list to answer. -What are the types of atoms that will combine with ionic bonds? -What types of atoms will form Metallic bonds? -What type of atoms will share electrons in Covalent bonds?

57 According to what you know about the different groups in the periodic table: -Which Groups of atoms will donate electrons? Groups 1,2,3 -Which Groups will receive electrons??? Groups 15, 16 and 17 -What types of atoms will form Ionic Bonds? metal and nonmetals -What types of atoms will form Metallic bonds? atoms of metals -What type of atoms will share electrons in Covalent bonds? Nonmetal and Nonmetal

58 Covalent bonds can be: POLAR NONPOLAR

59 **Covalent bonds can be: Polar and Nonpolar bonds Sometimes atoms will not share the electrons equally. This happens because some atoms attract the electrons more than others

60 Non Polar electrons in the bond are shared equally

61 Polar electrons in the bond are not shared equally

62 Electronegativity Electronegativity is the tendency of an atom to attract a bonding pair of electrons. Polar Bond - the shared pair of electrons stay closer to the atom that has a stronger pull (more electronegative) Molecule will have a + and a side ( weak charge)

63 EX: Water Oxygen has a higher electronegativity than Hydrogen. Oxygen will pull the bonding pair of Electrons. H 2 O polar bond

64 EX: Water polar molecule In a water molecule, the electrons spend more time around the oxygen atom. This molecule has a weak charge If a molecule has an uneven distribution of electrons this molecule is called polar. The atoms are united by polar covalent bonds

65 Carbon Dioxide: Nonpolar Molecule If a molecule has an even distribution of electrons it is called nonpolar. This molecule have no charge The bond that keep the atoms together is called a nonpolar bond

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67 Why is water considered the universal solvent? Because of it s polarity ( weak charge), water has the ability to dissolve most compounds ( more than any other solvent)

68 Like dissolve like??? Polar solvent will dissolve polar solutes Nonpolar solvents will dissolve nonpolar solutes Water can dissolve polar solutes and also ionic compounds because of its charge

69 OIL SPILL LAB

70 Like dissolve like??? Polar solvent will dissolve polar solutes Nonpolar solvents will dissolve nonpolar solutes

71 *Water and Oil Oils Spills *Why water and oils do not mix? *Because one molecule is polar and the other is nonpolar.

72 Water and Oil Surfactants or Dispersants are molecules that have one side that is polar and one nonpolar. Ex Detergents Will break oils into small droplets making it easier to wash away.

73 How do detergents work? Follow the principle Like dissolves like

74 The polar side of the detergent molecule is Hydrophilic attracted to the water The non-polar side is Hydrophobic- attracted to the oil (because both are nonpolar)

75 This can be important in the case of oil spills

76 Oil spills and some methods to clean it

77 Method 1 Booms and Skimmers floating devices that contain the oil

78 Containment of oil with booms

79 Recovery: use of floating devices called skimmers - are sponges that will absorb the oil

80 Method 2: Burning: problem smoke

81 Method 3: Sorbents

82 Method 4: Shoreline clean up

83 Method 5: Surfactants or Dispersants *Detergents are called surfactants or dispersants and will break oil into small droplets. *Small droplets of oil are easier to disperse in water, and are more rapidly biodegraded by microbes

84 the smaller the droplets the faster they are consumed by bacteria and the faster the oil will be removed from the area

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