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Forming Compounds:. Bonding. Bonding. When two atoms collide, valence electrons on both atoms interact. A chemical bond is created between the atoms if the valence electrons rearrange so that the new compound has less energy than before.
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Forming Compounds: Bonding
Bonding • When two atoms collide, valence electrons on both atoms interact. • A chemical bond is created between the atoms if the valence electrons rearrange so that the new compound has less energy than before. • The lowest energy arrangement of electrons is the same as the noble gases (8 valence electrons = happy)
Ionic • Ionic compounds are made up of cations and anions • the attractive force between oppositely charge ions (+ and -) is called an ionic bond • Nearly all ionic compounds are between metal cations and non-metal anions. • A compound with a crystalline shape is formed.
An atom can: • Give up electrons: forms an ion with a positive charge (cation) • Gain electrons: forms an ion with a negative charge (anion) • Share electrons: two atoms might share pairs of electrons (might share 1 pair, 2 pairs, or 3 pairs) • if 1 pair is shared= single bond • If 2 pairs are shared = double bond • If 3 pairs are shared = triple bond
Metals and Non-Metals • Remember: planetary models • Metals want to give away electrons • Ex. Na has 1 valence electron to give away • Ex. Mg has 2 valence electrons to give away • Ex. Al has 3 valence electrons to give away • Non-metals want to gain electrons • Ex. O has 2 valence electrons it wants to gain • Ex. Fluorine has 1 valence electron it wants to gain
Ionic Compounds: Properties • Relatively high melting points; large energy amount needed to break apart attraction forces in bond • Conduct electricity when molten or dissolved in water • Not electrical conductors in solid state
Molecular • Molecular compounds are substances composed of molecules; joined by covalent bonds • When atoms share a pair of electrons they are joined by a covalent bond • Electrons move back and forth between the outer energy levels of each atom in the covalent bond. • Most molecular compounds are made up of 2 or more non-metal elements
Molecular Compounds: Properties • Relatively low melting points because little energy is needed to break attractive forces in bond • Do not conduct electricity when solid or liquid or dissolved in water (aqueous, aq)
Diatomic Molecule • “di” means “two” • Diatomic molecule contains two atoms • Ex. Fluorine molecule F2 • These elements either have to: • Be bonded to themselves ex. F2, Cl2, H2 Or • Be bonded to another element ex. HBr, CO