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Published byPosy Patrick Modified over 9 years ago
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Chapter 7 and 8
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Valence electrons are responsible for the bonding between two atoms.
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In forming compounds, atoms tend to achieve the electron configuration of a noble gas. An octet is the set of eight electrons in the outermost energy level
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Atoms of metals tend to lose their valence electrons, leaving a complete octet in the next lowest energy level. Atoms of some nonmetals tend to gain electrons or share electrons with another nonmetal to achieve a complete octet. The ions that are produced when atoms of chlorine and other halogens gain electrons are called halides.
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Ionic compounds are usually composed of a metal cation and a nonmetal anion. Although they are composed of ions, ionic compounds are electrically neutral.
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Cations and anions have opposite charges and attract one another by means of electrostatic forces. The electrostatic forces that hold ions together in ionic compounds are called ionic bonds.
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A chemical formula shows the kinds and numbers of atoms in the smallest representative unit for a substance A formula unit is the lowest whole number ratio of ions in an ionic compound Ex. NaCl 1:1 Ex. MgCl 2 1:2
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Most ionic compounds are crystalline solids at room temperature Dissolve in water (soluble) Ionic compounds generally have high melting points Ionic compounds can conduct an electric current when melted or dissolved in water
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The valence electrons of metal atoms can be modeled as a sea of electrons Metallic bonds consist of the attraction of the free-floating electrons for the positively charged metal ions.
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Molecules and Molecular Compounds A covalent bond is described as the sharing of electrons between two atoms. Covalent compounds are a combination of two or more nonmetals
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A molecule is a neutral group of atoms joined together by covalent bonds. A diatomic molecule is a molecule consisting of two atoms of the same element. Br I N Cl H O F
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Molecular Compounds tend to have relatively lower melting and boiling points than ionic compounds Typically do not dissolve well in water Do not conduct electricity when dissolved in water
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A molecular formula is the chemical formula of a molecular compound A molecular formula shows how many atoms of each element a molecule contains.
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In covalent bonds, electron sharing usually occurs so that atoms attain the electron configurations of noble gases. Single Covalent bond: Sharing of one pair of electrons Double Covalent bond: Sharing of two pairs of electrons Triple Covalent bond: Sharing of three pairs of electrons
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A coordinate covalent bond occurs when one atom provides the shared electron pair Ex. Carbon Monoxide
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1. SUM THE VALENCE ELECTRONS FROM ALL ATOMS 2. Use the first atom of the chemical formula as the central atom (except hydrogen) and connect all other elements to that central atom with a single bond (---). 3. Complete the octets of the atoms bonded to the central atom. (Don’t forget that hydrogen only needs two electrons) 4. If there are not enough electrons to give the central atom an octet, try multiple bonds!.
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H2OH2O CF 4 CO 2
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Nonpolar covalent bond Atoms in the bond pull equally Bonding electrons are shared equally Ex. Diatomic molecules
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Polar Covalent bond Atoms in the bond pull with different strengths Bonding electrons are not shared equally Ex. HF
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Bond Polarity is based on the difference between two atoms electronegativity values Remember that electronegativity is the ability of an atom to attract electrons in a chemical bond.
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