Bonds can bend and stretch without breaking (bond lengths are averages)

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1 The Structure of Matter What are compounds? Two or more different elements bonded together by VALENCE ELECTRONS o The force that holds two atoms together The ability to write a formula, such as H2O, indicates a compound A compound always has the same chemical formula Types of Bonds Ionic: Opposing ions attract one another Covalent: Atoms share e - Metallic: Metal atoms bonding with other metal atoms Hydrogen: Bonding via hydrogen or polar molecules Bonds can bend and stretch without breaking (bond lengths are averages) Model of Compounds 1. Ball and Stick good for showing angles 2. Space-filling good for relative atomic sizes 3. Structural formula most commonly used Molecular Structure Chemical Properties Recall that ionization energy refers to how easily an atom loses an electron o Electron affinity refers to how much attraction an atom has for electrons Nobel gases have a full valence shell Thus, they have high ionization energy and low electron affinity o Elements tend to react to acquire the stable electron structure of a noble gas Formation of Ions Cations o By losing an electron, the atom has gained a positive charge (+1) and now has a different electron configuration Anion o Elements on the right side of table have high electron affinity and will therefore accept electrons forming a negative charge (-1) THE ATOM IS STILL THE SAME BUT NOW HAS A DIFFERENT ELECTRON CONFIGURATION Ionic Bonds A type of chemical bond that holds oppositely charged particles together in an ionic compound o Oxides: Metal and Oxygen (O) o Salts: Metal and non-metals Electrons are transferred, not shared o Ionic compounds are in the form of networks, not molecules During the formation of ionic bonds, the positive and negative ions are packed into a regular repeating pattern that balances the forces o This strong + to attraction in ionic bonds create a crystal lattice This causes all the cations to be completely surrounded by anions and vice versa

2 Properties of Ionic Compounds Crystalline solids STRONG BONDS High melting points High heats of vaporization Hard and brittle High boiling points High heats of fusion Many are soluble in water Poor conductors of heat and electricity when solid Good conductors of electricity when dissolved Creating ionic bonds is always exothermic o exo means out or exit, thermic means thermal or heat Heat or energy is released o If equal amount of energy were inserted into the bond, then the ionic bond would break The more negative the lattice energy, the stronger the force of attraction Larger absolute charges and smaller ions have a larger negative lattice energy Covalent Bonds A chemical bond that results from sharing of valence electrons o The shared electrons are considered to be part of the complete energy level of both atoms This is also known as a molecule o These tend to form between nonmetals o Covalent bond involves attractive and repulsive forces With molecules, it is endothermic to break bond and exothermic when building it, same as ionic o Covalent bonds can form two different types: Polar and non-polar Example of these can be found in the naturally occurring diatomic molecules Remember Mr. BrINClHOF Bromide (Br), Iodine (I), Nitrogen (N), Chlorine (Cl), Hydrogen (H), Oxygen (O), Fluorine (F) o Single Covalent Bonds This occurs when a single pair of electrons is shared The shared electron pair, or bonding pair, is represented by either a pair of dots or a line Lewis Dot Structures o Multiple Covalent Bonds Atoms can attain a noble-gas configuration by sharing more than one pair of electrons between two atoms Mostly formed by C, N, O and S This can be seen with double and triple covalent bonds Chemical Bonds Non-Polar Covalent bonds are between two identical nonmetal atoms Polar Covalent bonds are between two different nonmetal atoms Ionic bonds primarily form between nonmetals and reactive metals Ionic Character: Defined as the amount of sharing an atom does with electrons in a bond o Non-Polar bonds have 0% ionic character while ionic bonds have 100%. Polar and Non-Polar Recall: Electronegativity is the attraction of electrons via atoms bonded together in molecules If the difference in electronegativity between the bonded atoms is great enough, then the electrons will orbit more frequently around the atom with greater electronegativity o Equal sharing of electrons are non-polar molecules o Unequal sharing creates polar molecules

3 Polar molecules will have the uneven distribution of electrons because of the nucleus s pull o This creates POLES to the molecule similar to the Earth s North and South Poles e.g.: HF Hydrogen (2.2) vs Fluorine (4.0) Electrons will be found closer to fluorine than hydrogen, creating a negative pole are the fluorine nucleus Thus, a positive pole near hydrogen creating a DIPOLE molecule (two poles) Metallic Bonds Metallic bonding is the attraction between positive ions and surrounding freely mobile electrons o Electrons move freely between metal atoms An attraction between nuclei and neighboring electrons packs the metals in tightly, and allows electrons to move freely between o This is why metals conduct electricity Chemical Bond Glue Ionic Bonds What holds ionic bonds together? o The positive cation(s) and the negative anion(s) attraction via the electromagnetic force IMPORTANT: There are four universal forces o Strong Force: holds nucleus together (quarks or nucleon glue) o Electromagnetic Force: attracts opposite charges and poles o Weak Force: allows transmutation of nucleons o Gravity: mass attracts mass Chemical Bond Glue Covalent Bonds Van der Waal s Forces o What holds a polar covalent molecule together? The partial positive and partial negative charges via the electromagnetic force (again) Also known as dipole forces o Then what holds a non-polar covalent molecule together? London Dispersion Forces Electrons are always moving in their orbits and around the nuclei of atoms in the bonds At any point, there will be a congregation of electrons in one area more than another o This creates small TEMPORARY dipole forces that last fractions of fractions of a second Hydrogen Bonding This type occurs when hydrogen has a partial positive charge from the unequal distribution of electrons o Electronegativity The partial positive hydrogen will bind with a partial negative atom on another molecule o This connects water to water for example Dipole-Dipole Forces (a polar molecule binding to another polar molecule) Polyatomic Ions Groups of covalently bonded atoms that have either lost or gained electrons o Behave as ions (cations or anions) Parentheses group the atoms of a polyatomic ion and show that they act as any elemental ion o Cations are placed in front and anions behind *** The charge of the polyatomic ion is for the entire group, not just part of it. ***

4 Transition metal (TM) cations names must show their charge with ROMAN NUMERALS o Charge is determined mathematically (overall charge must be zero.) Lewis Dot Structures Each covalent bond is represented by a line in a Lewis dot structure o H 2 would be represented as H-H. o Atoms can form multiple covalent bonds if they need more than one electron to complete their valence shells. o Covalent bond involves attractive and repulsive forces o With molecules, it is endothermic to break bond and exothermic when building it o Numerical prefixes are used to name covalent compounds of two or more elements. Mono-, Di-, Tri-, Tetra-, Penta-, Hexa-, Hepta-, Octa-, Nona-, Deca- Elements are listed left to right on the periodic table and ends in ide. Formulas Empirical Formulas are the simplest form, or least common denominator for covalent molecular formulas. o Example: CH2O - Empirical formula for CH2O, C2H4O2, and C6H12O6. The structures of the molecules are different, so the behave very differently. C6H12O6 = Glucose (a type of sugar), C2H4O2 = Acetic acid (sourness of vinegar), & CH2O = Formaldehyde (embalming fluid) IUPAC Naming 1. First step is to identify the first atom in the compound. 2. If it is a metal, then the compound has an ionic bond and will have to use oxidation (+ or charges) numbers as well as Roman Numerals. * Be careful for polyatomic ions because these are IONS and thus ionic bonds as well. Covalent Bonds 3. If it is a non-metal, then the compound is a molecule and has covalent bonds. This will use the prefix system (1-10; mono, di, etc.) Ionic Bonds 4. After identifying it has an ionic bond, go to the back atom (or polyatomic ion) and identify the oxidation charge. (Nobel Gases = 0, Halogen = -1, Chalcogens = -2, Pnicogens = -3.) 5. Take this charge and multiply it by the total number of atoms (or polyatomic ions). This will get the total overall charge of all the anions. 6. The absolute value (or opposite + charge) will have to be found on the cation(s). This number will then be divided by the number of atoms (or polyatomic ions) to establish the cation s individual charge, or oxidation. 7. This charge will be the Roman Numeral assigned to the written name of the ionic compound. Basic Acids When identifying and naming acids, you are looking for two characteristics: 1. The compound/molecule will begin with hydrogen, H- 2. The number of following atoms will then determine the two ways of naming A binary acid (HCl, HBr, HI, etc.) will be called hydro- name of the anion with an ic ending, followed by acid Hydrochloric acid, hydrobromic acid, hydroiodic acid An oxyacid is when there is a polyatomic ion for the anion such as H2SO4 When this occurs, if it ends in ite then it s a ours ending and if it ends in ate then it is a ic ending.

5 Examples: HNO3 Nitric Acid; HNO2 Nitrous acid VSEPR: Valence Shell Electron Pair Repulsion Theory o The idea behind VSEPR is that covalent bonds and lone pair of electrons spread to the furthest distance they can from one another Covalent bonds consist of electrons and they have the same charge o Thus, VSEPR explains why molecules have their shapes o VSEPR Flow Chart Draw the Lewis Structure for the compound in question Count the number of things Follow the flow-chart Molecule Shapes o Tetrahedral Tetrahedral molecules look like pyramids with four faces and each point corresponds to an atom that's attached to the central atom Bond angles are degrees o Trigonal pyramidal It's like a tetrahedral molecule, except flatter Bond angles are degrees (it's less than tetrahedral molecules because the lone pair shoves the other atoms closer to each other) o Trigonal planar It looks like the hood ornament of a Mercedes automobile The bond angles are 120 degrees o Bent

6 They look bent Bond angles can be either 118 degrees for molecules with one lone pair or degrees for molecules with two lone pairs o Linear The atoms in the molecule are in a straight line This can be either because there are only two atoms in the molecule (in which case there is no bond angle, as there need to be three atoms to get a bond angle) or because the three atoms are lined up in a straight line (corresponding to a 180 degree bond angle)