Chapter 1: Electrons, Bonds, and Molecular Properties

What key element do organic compounds contain according to the introduction to organic chemistry?

Carbon

What are four examples of things made from organic compounds given on the organic chemistry introduction slide?

• Food

• Clothes

• Pharmaceuticals

• Plastics

What are pharmaceuticals?

Drugs or Medicines

In the ammonium cyanate-to-urea reaction shown in the organic chemistry introduction, which compound is inorganic and which is organic?

• Ammonium cyanate is inorganic

• Urea is organic

What happens when ammonium cyanate is heated in the reaction shown on the organic chemistry introduction slide?

It is converted into urea

What does the conversion of inorganic ammonium cyanate into organic urea demonstrate on the organic chemistry introduction slide?

An inorganic compound can be converted into an organic compound

What is organic chemistry?

The study of carbon-containing molecules and their reactions

What happens first when molecules undergo a chemical reaction according to the organic chemistry introduction slide?

The molecules collide

What happens to bonds during a chemical reaction?

Old bonds are broken and new bonds are made

What should you focus on when following an organic chemical reaction?

The movement of electrons

What do curved arrows represent in an organic reaction mechanism?

The movement of electrons

In the reaction HO⁻ + CH₃I → CH₃OH + I⁻, what new bond forms?

A C—O bond

In the reaction HO⁻ + CH₃I → CH₃OH + I⁻, what bond breaks?

The C—I bond

In the reaction HO⁻ + CH₃I → CH₃OH + I⁻, where do the electrons from the broken C—I bond go?

Onto iodine, producing I⁻

How does electron movement relate to bond changes during an organic reaction?

Electron movement causes new bonds to form and old bonds to break

Why is a molecular formula alone not enough to completely define a compound?

Compounds can have the same molecular formula but different ways of connecting their atoms

What are constitutional isomers?

Compounds with the same molecular formula but different atom connectivity

What molecular formula do dimethyl ether and ethanol share?

C₂H₆O

How are the atoms connected in dimethyl ether, CH₃—O—CH₃?

The oxygen is between the two carbons: C—O—C

How are the atoms connected in ethanol, CH₃—CH₂—OH?

The carbons are connected to each other, with oxygen at the end: C—C—O—H

Why are dimethyl ether and ethanol constitutional isomers?

They have the same molecular formula, C₂H₆O, but different atom connectivity

What is the boiling point of dimethyl ether on the slide?

−23°C

What is the boiling point of ethanol on the slide?

78.4°C

What does the dimethyl ether and ethanol example demonstrate about molecular structure?

Different atom connectivity can produce compounds with different physical properties even when the molecular formula is the same

What atoms are commonly bonded to carbon according to the slide?

• Nitrogen (N0

• Oxygen (O)

• Hydrogen (H)

• Halogens (X)

What does X represent when referring to halogens on this slide?

• F

• Cl

• Br

• I

How many bonds does carbon generally form?

4 bonds

How many bonds does nitrogen generally form?

3 bonds

How many bonds does oxygen generally form?

2 bonds

How many bonds does hydrogen generally form?

1 bond

How many bonds do halogens generally form?

1 bond

Match the common valence terms with their usual number of bonds: tetravalent, trivalent, divalent, and monovalent

Tetravalent = 4; trivalent = 3; divalent = 2; monovalent = 1

What quick pattern can be used to remember the usual number of bonds for C, N, O, H, and X?

C = 4, N = 3, O = 2, H/X = 1

What is a covalent bond?

A pair of electrons shared between two atoms

How many electrons are shared in one covalent bond?

2 electrons

What does the H-H represent?

A shared pair of electrons, or one covalent bond.

What molecule forms when two hydrogen atoms share a pair of electrons?

H₂

What is internuclear distance?

The distance between the nuclei of two atoms

What is the relationship between energy and stability?

Lower energy = greater stability

Why is the bonded H₂ molecule more stable than two separated H atoms?

The bonded H₂ molecule is at a lower-energy state

On the H—H energy vs. internuclear distance graph, what does the far right side of the graph represent?

Two H atoms far apart and not bonded

On the H—H energy vs. internuclear distance graph, what happens to energy and stability as the H atoms approach the proper bonding distance?

Energy decreases and stability increases

On the H—H energy vs. internuclear distance graph, what does the lowest point of the curve represent?

The lowest-energy, most-stable arrangement where the stable H—H bond forms

On the H—H energy vs. internuclear distance graph, what happens when the H atoms become too close together?

Their energy increases sharply

How are covalent bond formation, energy, and stability connected in H₂?

H atoms approach → H—H bond forms → lower-energy arrangement → greater stability.

In other words: the stable H—H bond occurs at the lowest-energy arrangement.

How does the H—H covalent bond connect to the earlier rule about hydrogen's common number of bonds?

Hydrogen generally forms one bond, and each hydrogen atom in H—H has exactly one covalent bond

How are potential energy and stability related in a covalent bond?

Lower potential energy = greater stability

What is the optimal bond length of H—H shown on the slide?

About 0.74 Å

What does the optimal H—H bond length represent?

The internuclear distance where the H—H bond has its lowest potential energy and greatest stability

What attractive force helps hold two covalently bonded H atoms together?

Attraction between the positively charged nuclei and negatively charged electrons

What repulsive force occurs between the nuclei of two H atoms?

The two positively charged nuclei repel each other

What repulsive force occurs between the electrons of two H atoms?

The two negatively charged electrons repel each other

What forces keep a covalent bond at its optimal bond length?

Attractive nucleus–electron forces and repulsive nucleus–nucleus and electron–electron forces

How do attractive and repulsive forces help establish the optimal length of a covalent bond?

Attractive forces pull the atoms together, while repulsive forces push like charges apart, producing an optimal distance where the bond has its lowest potential energy and greatest stability

Why does the potential energy of H₂ increase sharply when the two H atoms become too close together?

Repulsive forces between the two positively charged nuclei and between the two negatively charged electrons become too strong

What charge does a proton have?

+1 charge

What charge does a neutron have?

Neutral, or no charge

What charge does an electron have?

−1 charge

Where are protons and neutrons located in an atom?

In the nucleus

Where are electrons located in an atom?

In orbitals outside the nucleus.

What are valence electrons?

Electrons in the outermost shell of an atom

Why are valence electrons the main focus when studying covalent bonding?

Valence electrons are involved in bonding.

How many total electrons does a neutral carbon atom have?

6 electrons

How many valence electrons does carbon have?

4 valence electrons

How are valence electrons connected to covalent bond formation?

Valence electrons are the electrons involved in bonding and can be shared between atoms to form covalent bonds

How do carbon's total number of electrons and number of valence electrons differ?

Carbon has 6 total electrons, but only 4 of them are valence electrons in its outermost shell

What are the two ways shown on the slide to determine the number of valence electrons?

Analyze the electron configuration, or use the Group A number for Group A elements

How can an electron configuration be used to determine the number of valence electrons?

Find the outermost shell and count the electrons in it

For Group A elements, how does the group number relate to the number of valence electrons?

Group number = number of valence electrons

How many valence electrons does a Group 4A element have?

4 valence electrons

How many valence electrons does a Group 6A element have?

6 valence electrons

How many valence electrons does a Group 7A element have?

7 valence electrons

Based on its position in Group 4A of the periodic table, how many valence electrons does carbon have?

4 valence electrons

Based on its position in Group 6A of the periodic table, how many valence electrons does oxygen have?

6 valence electrons.

Based on its position in Group 7A of the periodic table, how many valence electrons does chlorine have?

7 valence electrons

Does the Group A number shortcut for counting valence electrons apply to the transition metals on this slide?

No. The slide specifies the shortcut for Group A elements only

How do carbon's electron arrangement and its Group A number both show that carbon has 4 valence electrons?

Carbon has 4 electrons in its outermost shell, and carbon is also in Group 4A, which corresponds to 4 valence electrons.

What do the dots represent when drawing individual atoms for a simple Lewis structure?

Valence electrons

What is the first step for drawing a simple Lewis structure according to the slide?

Draw the individual atoms using dots to represent their valence electrons.

What is the second step for drawing a simple Lewis structure according to the slide?

Put the atoms together so they share pairs of electrons to make complete octets

How many valence electrons does nitrogen have before forming NH₃?

5 valence electrons

How many valence electrons does each hydrogen atom have before forming NH₃?

1 valence electron

What does a shared pair of electrons between N and H represent in the Lewis structure of NH₃?

One N—H covalent bond

How many N—H covalent bonds are present in the Lewis structure of NH₃?

3 N—H covalent bonds

What is a lone pair of electrons?

A pair of valence electrons that is not shared in a covalent bond.

How many lone pairs does nitrogen have in the Lewis structure of NH₃?

1 lone pair

How does knowing an atom's valence electrons help you draw a Lewis structure

The valence electrons are drawn as dots and show which electrons can be shared when the atoms form covalent bonds.

What is the difference between a bonding pair and a lone pair of electrons in a Lewis structure?

A bonding pair is shared between two atoms in a covalent bond, while a lone pair remains on one atom and is not shared

What is an anion?

A negatively charged atom

What is a cation?

A positively charged atom

What does it mean for an atom to be neutral?

The atom has no overall positive or negative charge

What two quantities are compared to determine the formal charge of an atom in a molecule?

he number of valence electrons the atom owns based on its bonding pattern and the number of valence electrons it needs to be neutral.

What determines how many valence electrons an atom owns when determining formal charge?

Its bonding pattern in the molecule

How does knowing an atom's valence electrons help when determining its formal charge?

Formal charge is determined by comparing how many valence electrons the atom owns in the molecule with how many valence electrons it needs to be neutral

How do Lewis structures connect to determining formal charge?

A Lewis structure shows an atom's bonding pattern, which is used to determine how many valence electrons the atom owns when assigning formal charge

How many valence electrons does carbon need to be neutral?

4 valence electrons

Why does carbon need 4 valence electrons to be neutral?

Carbon is in Group 4A

How many electrons surround the carbon atom in the Lewis structure shown on the slide?

8 electrons.

When determining formal charge, how many electrons does carbon own from each covalent bond in the structure shown?

1 electron from each bond

How does the sharing of electrons in covalent bonds explain why carbon owns only 4 of the 8 electrons surrounding it?

Each covalent bond contains a shared pair of electrons, so carbon owns one electron from each of its four bonds