Chemistry Isotopes and Chemical Bonds

Isotopes

• Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.
• The number of protons determines the atomic number of an element.
• The number of protons and neutrons together determine the mass number of an atom.
• Carbon has an atomic number of 6, meaning it has 6 protons in its nucleus.
• Most carbon atoms also have 6 neutrons, giving them a mass number of 12, written as ¹²C.

Valence Electrons

• The valence shell is the outermost shell of an atom.
• Valence electrons are the electrons in the valence shell that an atom uses to form chemical bonds.
• The number of valence electrons an atom has is equal to its group number on the periodic table.
• For example, carbon (group IVA) has four valence electrons, while oxygen (group VIA) has six.

Chemical Bonds: The Octet Rule

• Ionic bonds are formed by the transfer of electrons between atoms.
• Covalent bonds are formed by the sharing of electrons between atoms.
• The octet rule states that atoms tend to achieve a configuration where their valence shell contains eight electrons.
• This rule is a way to predict how atoms will bond together to form molecules.

Lewis Structures

• Lewis structures are diagrams that show the connections between atoms in a molecule using only the valence electrons.
• Main group elements have the same number of valence electrons as their group number.
• If a structure is an anion, add one electron for each negative charge.
• If a structure is a cation, subtract one electron for each positive charge.
• When drawing Lewis structures, aim to give each atom the electron configuration of a noble gas, which typically has eight valence electrons.

Resonance Theory

• Resonance theory is used to describe molecules or ions where a single Lewis structure is inadequate.
• Two or more equivalent resonance structures can be drawn to represent the same molecule.
• The real molecule or ion is a hybrid of all the resonance structures.
• Resonance structures are not real structures but are used to better represent the molecule or ion.

Hybridization: sp³ Hybridization

• Hybridization is the mixing of atomic orbitals to form new hybrid orbitals with different shapes and energies.
• sp³ hybridization occurs when one s orbital and three p orbitals combine to form four sp³ orbitals.
• Each sp³ orbital has a tetrahedral shape.
• Methane (CH₄) is an example of a molecule with sp³ hybridized carbon.

Hybridization: sp² Hybridization

• sp² hybridization occurs when one s orbital and two p orbitals combine to form three sp² orbitals.
• These sp² orbitals are planar and have a trigonal planar shape.
• Ethene (C₂H₄) is an example of a molecule with sp² hybridized carbons.
• The sp² hybridized carbons in ethene form a double bond consisting of a sigma bond and a pi bond.

Restricted Rotation and the Double Bond

• Restricted rotation exists about a double bond due to the strength of the pi bond.
• Rotation around the double bond breaks the pi bond and requires significant energy.

Cis-Trans Isomerism

• Cis-trans isomerism arises due to restricted rotation around a double bond.
• Cis isomers have the same substituents on the same side of the double bond.
• Trans isomers have the same substituents on opposite sides of the double bond.
• Cis-trans isomerism is only possible for disubstituted alkenes, which have two different substituents on each carbon of the double bond.

This quiz covers fundamental concepts of isotopes, valence electrons, and chemical bonds, including the octet rule. You will explore how protons and neutrons define atomic structure, and the significance of valence electrons in bond formation. Test your understanding of these essential chemistry topics!