Notes 3- Chemical Bonds, Isotopes, Ions

Bonding properties Effect of electrons chemical behavior of an atom depends on its electron arrangement depends on the number of electrons in its outermost shell, the valence shell Octet rule- atoms “want” to have 8 electrons in the valence shell How does this atom behave?

Bonding properties How does this atom behave?

Chemical reactivity Atoms tend to: Complete a partially filled outer (valence) electron shell or Empty a partially filled outer (valence) electron shell 8 is the magic number of valence electrons!! This tendency drives chemical reactions

Chemical Bonds Strongest Bonds: 1. Covalent Bonds: two atoms need one electron, so they share a pair of electrons Polar Covalent Bond: electrons are shared unevenly ex) H2O- oxygen has the stronger “attraction” for electrons than hydrogen. Nonpolar Covalent Bond: electrons are shared equally between the atoms. ex) O2

Chemical Bonds Double covalent bonds Two atoms can share more than one pair of electrons double bonds (2 pairs of electrons) triple bonds (3 pairs of electrons) Very strong bonds

Chemical Bonds 2. Ionic Bonds: electron is transferred from one atom to another Forms one (+) and one (-) ion (+) = cation (-) = anion Weaker than covalent bond Generally occur between a metal and a nonmetal

Isotopes # of neutrons varies, but same # of protons (same element, different mass) Radioactive isotopes used as biological tracers (follow molecules, medical diagnoses) Some are unstable- can also be a biological hazard

Ions Atom with a charge Remember... Cation= positive charge Anion= negative charge

Na Ions 11 +1 23 How many protons does sodium have? How many neutrons does sodium have? How many electrons does sodium have? 11 Na +1 23

Ag Ions 47 -2 108 How many protons does silver have? How many neutrons does silver have? How many electrons does silver have? 47 Ag -2 108