AS.030.205 Chapter 1: Chapter 1, Organic Chemistry
Chapter 1: Remembering General Chemistry: Electronic Structure and
Bonding
Organic compound: compounds that are based on carbon, consists of atoms held together
by covalent bonds
Why carbon?
Carbon is in center of second row of elements, therefore it neither readily gives up
nor readily accepts electrons; it instead shares electrons with various kinds
of atoms including itself.
Covalent bonds form when two atoms share electrons and break when two atoms no
longer share electrons.
1.1: The Structure of an Atom
Atom: consists of tiny dense nucleus surrounded by electrons that are spread throughout a
relatively large volume of space around the nucleus called an electron cloud
Nucleus: contains positively charged protons and uncharged neutrons, so it is positively
charged, holds most of the atom’s mass
Electrons: negatively charged particles that move continuously, has kinetic energy that
counteracts the attractive force of the positively charged protons that pull the
negatively charged electrons toward the nucleus
Electron cloud: holds most of the volume of the atom
Atomic number: number of protons in its nucleus
Mass number: sum of its protons and neutrons
Isotope: atoms with the same atomic number but differing mass numbers
Atomic mass: weighted average of isotopes in the element
*atomic mass unit (amu) = 1/12 the mass of 12C
Molecular mass: sum of the atomic masses of all the atoms in the molecule
Molecule: a group of two or more atoms held together by bonds
1.2: How the Electrons in an Atom are Distributed
Electrons first perceived to be particles that orbit the nucleus, but de Broglie showed that
electrons also have wave-like properties
Quantum mechanics: characterizes the motion of an electron around a nucleus using the
same mathematical equations that describe other wave motions
Atomic orbital: subshell within each shell, has a characteristic shape and energy and
occupies a characteristic volume of space
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Degenerate orbitals: orbitals that have the same energy (1 s orbital, 3 degenerate p
orbitals, 5 degenerate d orbitals, 7 degenerate f orbitals)
Pauli exclusion principle: max of 2 electrons can coexist in an atomic orbital
Ground-state electronic configuration: describes the atomic orbitals occupied by the
atom’s electrons when they are all in the available orbitals with the lowest energy
Excited-state electronic configuration: energy is applied to an atom in the ground state,
making one or more electrons jump into a higher-energy orbital, putting the atom in
an excited state
Aufbau principle (Aufbau is German for ‘building up’): an electron always goes into the
available orbital with the lowest energy
Pauli exclusion principle: no more than two electrons can occupy each atomic orbital,
and the two electrons must be of opposite spin
Hund’s rule: when there are two or more atomic orbitals with the same energy, an
electron will occupy an empty orbital before it will pair up with another electron
*when putting electrons into degenerate orbitals, the electrons can be put in any one of the
degenerate orbitals as long as Hund’s rule is obeyed as well.
Valence electrons: electrons in an atom’s outermost shell, participate in chemical bonding
Core electrons: electrons in inner shells (below the outermost shell), do not participate in
chemical bonding
*elements in the same column of the periodic table have similar chemical properties
because they have the same number of valence electrons
1.3: Covalent Bonds
G. N. Lewis’s theory (Octet rule): an atom is most stable if its outer shell is either filled or
contains 8 electrons, and it has no electrons of higher energy; an atom will give up,
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accept, or share electrons to achieve a filled outer shell or an outer shell that
contains 8 electrons
Ion: species that carries a charge
Electronegative: readily acquires electrons
Hydrogen ion: loss of sole electron makes positively charged hydrogen ion (proton)
Hydride ion: negatively charged hydrogen (when a hydrogen atom gains an electron)
Covalent bond: bond formed as a result of sharing electrons between two nuclei (O forms
2, N forms 2, C forms 4)
Electronegativity: measure of the ability of an atom to pull electrons towards itself
Nonpolar covalent bond: covalent bond between atoms with essentially the same
electronegativity; electronegativity difference between the bonded atoms is less
than 0.5; the atoms share the bonding electrons equally
Polar covalent bond: covalent bond between atoms with different electronegativities;
electronegativity difference between bonded atoms is between 0.5 and about 1.9;
bonding electrons are unsymmetrically distributed b/c the bonding atoms have
sufficiently different electronegativities (partial +/- charges); direction of bond
polarity indicated with arrow in direction of electrons being pulled (towards
negative)
Electrostatic attraction: an attractive force between opposite charges; electronegativity
difference is greater than 1.9, so the atoms do not share electrons; electrons are
transferred from one atom to the other (ex. NaCl)
Ionic compound (salt): formed when an element on the left side of the periodic table
transfers one or more electrons to an element on the right side of the periodic table
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Document Summary
Chapter 1: remembering general chemistry: electronic structure and. Organic compound: compounds that are based on carbon, consists of atoms held together by covalent bonds. Carbon is in center of second row of elements, therefore it neither readily gives up nor readily accepts electrons; it instead shares electrons with various kinds of atoms including itself. Covalent bonds form when two atoms share electrons and break when two atoms no longer share electrons. Atom: consists of tiny dense nucleus surrounded by electrons that are spread throughout a relatively large volume of space around the nucleus called an electron cloud. Nucleus: contains positively charged protons and uncharged neutrons, so it is positively charged, holds most of the atom"s mass. Electrons: negatively charged particles that move continuously, has kinetic energy that counteracts the attractive force of the positively charged protons that pull the negatively charged electrons toward the nucleus. Electron cloud: holds most of the volume of the atom.
