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Ionic & Covalent Bonding

  • Lewis Dot Structure

    • represents electrons as dots in dot structures

    • the valence electrons of main-group elements are represented as dots surrounding the element symbol

    • dots are filled on all 4 sides before pairing - Helium is the only exception

    • octet rule - atoms with 8 valence electrons - which are particularly stable

      • exclusions: hydrogen, lithium, beryllium

      • achieve stability when it has 2 electrons in valence shell

    • chemical bonds involves the sharing or transfer of electrons to attain stable electron configuration

      • ionic bond - electrons are transferred

      • covalent bond - electrons are shared

    • stable configuration - eight electrons in the valence shell

  • Ionic Bonds

    • metals bond with nonmetals - electrons are transferred from the metal to the nonmetal

    • metal becomes a cation

    • nonmetal becomes an anion

    • attraction between cation + anion → ionic compound

    • metal/cation always comes first in the chemical formula

    • properties

      • generally crystalline solid at room temp

      • strong bond due to large attractive forces

      • high melting point due to strong bond

      • generally soluble in water

      • conduct electricity in molten or dissolved state because ions move freely

  • Covalent Bonds no ions

    • when nonmetals bond with other nonmetals

    • electrons are shared

    • share valence electrons in order to attain octets

      • bonding pair electrons : electrons shared between two atoms

      • lone pair / nonbonding : electrons not involved in bonding

    • properties

      • generally gas at room temp

      • weaker bond than ionic compounds

      • low melting point due to weak bonds

      • generally insoluble in water

      • do not conduct electricity

  • chemical formula - shows the numbers of atoms of each element in the smallest representative unit of a substance

  • formula unit - the lowest whole number ratio of ions in an ionic compound

  • Polyatomic Ions

    • molecule with a charge

    • atoms bonded covalently

    • metal has to be present during bonding

  • Polarity

    • electronegativity - ability of an element to attract electrons within a covalent bond

    • dipole moment - has a partial negative charge (δ-) and a partial positive charge (δ+)

      • result of uneven electron sharing

      • the element with the highest electronegativity has the partial negative charge

    • the magnitude of the dipole moment and the polarity of the bond depend on the electronegativity difference between the two elements in the bond

      • 0≤x≤.4 - nonpolar covalent

      • .4<x≤2.0 - polar covalent

      • 2.0≤x≤3.3 - ionic

      • if on 2.0 - depends on the presence of a metal

    • covalent bonds

      • polar - unequal sharing

      • nonpolar - equal sharing

    • flourine has the most electronegativity with 4.0

  • Predicting the Shape of Molecules - VSEPR

    • Valence Shell Electron Pair Repulsion

    • idea that electron groups - lone pairs + single/multiple bonds - repel each other

    • this repulsion between the negative charges of electron groups on the central atom determines the geometry of the molecule

  • transition metals can form multiple ions except

    • zinc +2

    • cadmium +2

    • silver +1

Ionic & Covalent Bonding

  • Lewis Dot Structure

    • represents electrons as dots in dot structures

    • the valence electrons of main-group elements are represented as dots surrounding the element symbol

    • dots are filled on all 4 sides before pairing - Helium is the only exception

    • octet rule - atoms with 8 valence electrons - which are particularly stable

      • exclusions: hydrogen, lithium, beryllium

      • achieve stability when it has 2 electrons in valence shell

    • chemical bonds involves the sharing or transfer of electrons to attain stable electron configuration

      • ionic bond - electrons are transferred

      • covalent bond - electrons are shared

    • stable configuration - eight electrons in the valence shell

  • Ionic Bonds

    • metals bond with nonmetals - electrons are transferred from the metal to the nonmetal

    • metal becomes a cation

    • nonmetal becomes an anion

    • attraction between cation + anion → ionic compound

    • metal/cation always comes first in the chemical formula

    • properties

      • generally crystalline solid at room temp

      • strong bond due to large attractive forces

      • high melting point due to strong bond

      • generally soluble in water

      • conduct electricity in molten or dissolved state because ions move freely

  • Covalent Bonds no ions

    • when nonmetals bond with other nonmetals

    • electrons are shared

    • share valence electrons in order to attain octets

      • bonding pair electrons : electrons shared between two atoms

      • lone pair / nonbonding : electrons not involved in bonding

    • properties

      • generally gas at room temp

      • weaker bond than ionic compounds

      • low melting point due to weak bonds

      • generally insoluble in water

      • do not conduct electricity

  • chemical formula - shows the numbers of atoms of each element in the smallest representative unit of a substance

  • formula unit - the lowest whole number ratio of ions in an ionic compound

  • Polyatomic Ions

    • molecule with a charge

    • atoms bonded covalently

    • metal has to be present during bonding

  • Polarity

    • electronegativity - ability of an element to attract electrons within a covalent bond

    • dipole moment - has a partial negative charge (δ-) and a partial positive charge (δ+)

      • result of uneven electron sharing

      • the element with the highest electronegativity has the partial negative charge

    • the magnitude of the dipole moment and the polarity of the bond depend on the electronegativity difference between the two elements in the bond

      • 0≤x≤.4 - nonpolar covalent

      • .4<x≤2.0 - polar covalent

      • 2.0≤x≤3.3 - ionic

      • if on 2.0 - depends on the presence of a metal

    • covalent bonds

      • polar - unequal sharing

      • nonpolar - equal sharing

    • flourine has the most electronegativity with 4.0

  • Predicting the Shape of Molecules - VSEPR

    • Valence Shell Electron Pair Repulsion

    • idea that electron groups - lone pairs + single/multiple bonds - repel each other

    • this repulsion between the negative charges of electron groups on the central atom determines the geometry of the molecule

  • transition metals can form multiple ions except

    • zinc +2

    • cadmium +2

    • silver +1

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