Table of Contents Chapter: Atomic Structure and Chemical Bonds Section 1: Why do atoms combine? Section 2: How Elements Bond
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.
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
The atom has: 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.
Atoms Charges Nucleus has (+) charge = protons Electrons have a (-) charge and move randomly in the electron cloud
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.
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
Energy levels are also called shells, valence shells
Energy Levels and Number of electrons Each energy level can hold a different number of electrons ( 2, 8, 18 ) some exceptions
Energy Levels Electrons are attracted by the nucleus so USUALLY the electrons will occupy the energy levels closer to the nucleus first.
**The electrons in the outermost energy level always have the greatest energy and are less stable. **Less stable means that this atom 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.
***The electrons that occupy the last energy level are called valence electrons and are the electrons involved in chemical reactions
Valence Electrons in the Periodic table Groups handout with note taking wkst Elements in Group 1: 1 valence electron 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
Energy Levels 2n2 formula used to calculate the maximum number of electrons an energy level can hold n = the number of the energy level.
Octet Rule ** 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 ( these atoms have one energy level only page 467 fig 5) *In MANY CASES: if the last energy level is complete, the atom is stable
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.
-Atoms with 1, 2 or 3 electrons in the outer energy level will lose electrons to become stable (atoms in groups 1,2 and 3) -Atoms with 5, 6 and 7 electrons in the outer energy level, will receive electrons to become stable (atoms in groups 5,6 and 7) - Atoms with 4 usually share electrons
EX: The atoms in Group 1 need to donate one electron and the atoms in the Group 17 need to receive one electron. They are the most reactive in the periodic table and often react with each other forming salts. Group 1 Alkali Metals Group 17 Halogens
Representing Atomic Configuration or Structure There are 2 ways we can represent the electron configuration of atoms: Bohr Model of the atom as seen on page 467 Lewis Structure also called Electron Dot Diagram
Atom Diagrams Lewis Structure or Electron Dot Diagram Bohr Model of the atom
Bohr Model, shows the distribution of all the electrons of an atom How to do the Bohr Model: Ex: Oxygen - Find the atomic number - Find the number of electrons - Distribute the electrons in the energy levels - check the list of valence electrons to see if it is correct Draw the Bohr model for Sodium, Phosphorus, Fluorine and Hydrogen
Sodium Let s do the Bohr Model for Phosphorus, Fluorine and Hydrogen
Phosphorus atomic number - 15
Fluorine Atomic number - 9
Hydrogen atomic number = 1 one electron in the last shell, very reactive
Electron dot diagram or Lewis Structure - shows 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
Steps to do an Electron Dot Diagram: Find the group the atom belongs to in the PT Refer to your Number of Valence Electrons per group handout and find out the number of valence electrons in an atom of that element 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.
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
CHAPTER 16 - SECTION 2 How elements bond: Chemical bond is the force that keeps two atoms together. We already studied that: Atoms can gain, donate or share electrons
There are 3 types of bonds between atoms Ionic Bonds Covalent Bonds Metallic Bonds
In Ionic Bonds: one atom gives an electron, the other receives
In Covalent Bonds: atoms will share electrons
**Bonds Atoms form bonds with other atoms using the electrons in their outer energy levels. 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.
Symbols for Compounds Elements are represented by symbols and these symbols are letters molecules are represented by symbols and numbers. (molecules are combinations of atoms) Ex: H2O 2 atoms of Hydrogen and one of oxygen The number 2 is called a subscript H2O is called a chemical formula (for water)
Chemical Formulas Importance of the subscript CO carbon monoxide / CO2 carbon dioxide Water H2O / Hydrogen Peroxide - H2O2
**IMPORTANT TO REMEMBER Ionic bonds bonds between metals and nonmetals or metalloids, forming Ionic Compounds Covalent bonds bonds between nonmetals or metalloids, forming molecular compounds Metallic bonds bonds between metals, forming metallic compounds
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
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)
Ions Formation Na+ and Cl- - Sodium becomes a + ion - Chlorine becomes a ion (receives one electron from Sodium) - Na and Cl combine forming NaCl (sodium chloride)
Chemical Reaction representation using the Electron Dot Diagram This is Ionic Bond and NaCl is an ionic compound.
More Gains and Losses Can elements lose or gain more than one electron? Mg can lose 2 and Oxygen can gain 2 electrons to become stable. When this happens, magnesium oxide (MgO) is formed and is an ionic compound
More Gains and Losses Can elements lose or gain more than one electron? EX: Magnesium and Oxygen 1) where can you find these atoms in the PT? Which Groups? 2) How many electrons do they have in the outer energy level? 3) Which one will lose and which one will gain?
Practice: Ionic bonds
Show the transfer of electrons in the following combinations Na + Cl Mg + Br Cl + Ca Ca + O K+F K +O Mg + I Be + S Al + Br 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)
Covalent Bonds electron sharing because of the number of electrons in their outer levels, some atoms will share electrons Covalent Bonds happen between nonmetals
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
3 types of Covalent bonds: single, double and triple
6 and 4 atoms are too many to donate or gain so these atoms will share electrons
Double Bond CO2
Triple Bond N has 5 e- in the last energy level
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 (N2) 3)C+O (CO2) 8)H+O (H2O) 4)N+O (N2O2) 9)S + O 5)H+F 10)N + H (NH3)
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.
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.
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?
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
**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
Non Polar electrons in the bond are shared equally
Polar electrons in the bond are not shared equally
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)
EX: Water Oxygen has a higher electronegativity than Hydrogen. H2O in water hydrogen and oxygen are united by a polar bond
EX: Water is a 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
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
Nitrogen molecule is nonpolar
Why is water considered the universal solvent? Because of its polarity ( weak charge), water has the ability to dissolve most compounds ( more than any other solvent)
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
*Water and Oil Oils Spills *Why water and oils do not mix? *Because one molecule is polar and the other is nonpolar.
How do detergents work? Follow the principle Like dissolves like
Water and Oil Surfactants or Dispersants are molecules that have one side that is polar and one nonpolar. Ex Detergents Detergents will break oils into small droplets making it easier to wash away.
The polar side is Hydrophilic attracted to the water The non-polar side Hydrophobic- attracted to the oil
This can be important in the case of oil spills
Oil spills and some methods to clean it
Method 1 Booms and Skimmers floating devices that contain the oil
Containment of oil with booms
Recovery: use of floating devices called skimmers - are sponges that will absorb the oil
Method 2: Burning: problem smoke
Method 3: Sorbents
Method 4: Shoreline clean up
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 degraded by microbes
the smaller the droplets the faster they are consumed by bacteria and the faster the oil will be removed from the area
Dispersants Small oil droplets will be consumed by bacteria