Chemistry Chapter 4: Molecules and Isotopes

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Questions and Answers

What is the bond angle between hydrogen atoms in a methane (CH4) molecule?

109.5 degrees (correct)

90 degrees

180 degrees

120 degrees

What molecular geometry best describes a methane (CH4) molecule?

Trigonal planar

Tetrahedral (correct)

Linear

Bent

Which statement best describes the relationship between electronegativity and the distance from the nucleus?

Electronegativity increases as the distance between electrons and the nucleus decreases. (correct)

Electronegativity increases as the distance between electrons and nucleus increases.

Electronegativity is independent of the distance between the electrons and the nucleus.

Electronegativity decreases as the distance between electrons and nucleus decreases.

When does a polar covalent bond form between two atoms?

When the difference in electronegativity is between 0.4 and 1.7 Signup and view all the answers

What characteristic of an atom determines its electronegativity?

The atomic number and distance of valence electrons from the nucleus Signup and view all the answers

What is the primary difference between isotopes of the same element?

The number of neutrons. Signup and view all the answers

Which subatomic particle primarily dictates the element's identity?

Protons Signup and view all the answers

What is a radioisotope?

An unstable isotope that emits radioactivity while decaying. Signup and view all the answers

Which of the following is a true statement regarding the behavior of isotopes during chemical reactions?

They react the same way because they have the same number of protons and electrons. Signup and view all the answers

If the atomic number of an atom is 8 and its atomic mass is 16, how many neutrons does it have?

8 Signup and view all the answers

What is the main use of Carbon-14 in the context of fossils?

Determining the absolute age of fossils Signup and view all the answers

What is the approximate percentage of organic compounds, consisting mainly of Carbon, Hydrogen, Oxygen, and sometimes Nitrogen, in a living organism?

96% Signup and view all the answers

Where are electrons primarily located within an atom?

In outer orbitals around the nucleus Signup and view all the answers

What is the maximum number of electrons that the second electron shell of an atom can hold?

8 Signup and view all the answers

Which electron shell is closest to the nucleus of an atom?

The 1st shell. Signup and view all the answers

What do the letters 's', 'p', 'd', and 'f' represent in the context of electron shells?

They represent the different shapes of the atomic orbitals within a shell. Signup and view all the answers

What are valence electrons?

Electrons located in the outermost shell of an atom. Signup and view all the answers

How many electrons can a 2p orbital hold?

6 Signup and view all the answers

Which of the following best describes why atoms with 3 or fewer valence electrons tend to lose electrons?

To become positively charged cations. Signup and view all the answers

What type of bond is formed when atoms share one or more pairs of valence electrons?

Covalent bond Signup and view all the answers

What is electronegativity?

The measure of an atom’s attraction for additional electrons. Signup and view all the answers

Study Notes

General Chemistry

Matter makes up everything in the universe, including living organisms
An element is a pure substance that cannot be broken down
An atom is the smallest particle of an element
Atoms bond together to form molecules and compounds.

Organic Compounds

Organic compounds are made up of C, H, O, and sometimes N
These compounds make up 96% of the mass of living organisms
The other 4% consists primarily of Ca, P, K, S, Na, Cl, and Mg

Atomic Structure

Atoms are composed of three subatomic particles: protons, neutrons, and electrons
Protons determine the identity of an atom
An atomic mass is equal to the sum of protons and neutrons
A proton has a positive charge (+), a neutron is neutral, and an electron is negative (-)
Protons and neutrons are located in the nucleus
Electrons are located in orbitals outside the nucleus
The atomic number of an atom shows the number of protons
The atomic mass of an atom shows the number of protons and neutrons

Isotopes and Radioisotopes

Isotopes are atoms of the same element with the same number of protons but a different number of neutrons
Isotopes behave the same way in chemical reactions because they have the same number of protons and electrons
Radioisotopes are unstable isotopes that decay (break down)
Radioisotopes are used to date fossils by comparing the ratio of 14C to 12C as the half-life of 14C is 5730 years.

Electron Arrangements

Electrons are arranged in orbitals around the nucleus
Electron orbitals are grouped into shells (energy levels)
The first shell holds 2 electrons, the second 8, and the third 18
Shells are designated by letters: 1s, 2s, 2p, 3s, and 3p
The energy levels are further described by regions (s, p, d, f).

Chemical Bonds

Ionic bonds form when atoms transfer electrons
Covalent bonds form when atoms share electrons
The strength of a covalent bond is determined by the electronegativity of the atoms involved
Electronegativity is the measure of an atom's attraction for additional electrons

Polar Molecules

Polar molecules have an uneven distribution of charge
The more electronegative an atom, the more strongly it attracts electrons
Electronegativity differences between the component atoms determine the polarity of a covalent molecule

Intermolecular Forces

Intermolecular forces are forces of attraction between molecules
Hydrogen bonds are a type of intermolecular force that involves a partially positively charged hydrogen atom and a partially negatively charged atom in another molecule
Individual hydrogen bonds are weak but collectively strong and are important for the 3-D structure of biological molecules

Chemical Reactions of Biological Importance

Condensation (dehydration) reactions combine monomers into polymers while removing water
Hydrolysis reactions break polymers into monomers by adding water

Oxidation and Reduction (Redox) Reactions

Oxidation → loss of electrons
Reduction → gain of electrons
In biological systems, these reactions must occur together

Properties of Water

Water molecules associate via hydrogen bonding
Water has a high specific heat capacity, meaning that it takes more energy to raise the temperature of water compared to other substances
Water has a high capacity to absorb energy when it evaporates, making it useful in temperature regulation, such as sweating.

Aqueous Solutions

Water is a solvent in many biological processes
Polar or charged molecules, or hydrophilic (water loving) molecules dissolve easily in water
Non-polar molecules, or hydrophobic (water fearing) molecules, do not readily dissolved in water

Water as a Solvent

Water molecules surrounding and forming hydration spheres around molecules dissolve
Small molecules (and ions) dissolve easily into water molecules

pH and Acids and Bases

The pH scale measures acidity and basicity of a solution on a scale from 0 to 14.
A pH < 7 is an acid; a pH > 7 is a base
The concentration of H+ ions determines the acidity of a solution
Buffers resist changes in pH

Carbon-Based Molecules

Carbon atoms have 4 valence electrons → capable of forming 4 covalent bonds
Carbon forms the backbone of most large biological molecules in living organisms
The variety of carbon molecules is due to these bonds
Many molecules important to living organisms are called biomolecules
This includes carbohydrates, lipids, proteins, and nucleic acids.

Carbohydrates

Monosaccharides are simple sugars (e.g., glucose, fructose, galactose)
Disaccharides are formed by joining two monosaccharides (e.g., sucrose, lactose, maltose)
Polysaccharides are long chains of monosaccharides (e.g., starch, glycogen, cellulose)

Lipids

Fats store energy
Phospholipids form the membranes that surround cells
Steroids are important signalling molecules

Proteins

Proteins are composed of amino acids
Amino acids are the building blocks of proteins (20 common)
Proteins carry out a variety of functions in cells

Nucleic Acids

DNA stores genetic information
RNA helps in protein synthesis

Cell Structures

Organelles are internal, functional structures of cells (e.g. mitochondria, chloroplasts, nuclei)
Cells contain components for metabolism, energy production, and reproduction

Cellular Respiration

Breakdown of sugars (and other fuels) to produce ATP
Aerobic respiration requires oxygen
Anaerobic respiration does not require oxygen and typically produces less ATP
The process of aerobic respiration occurs in 3 stages: glycolysis, pyruvate oxidation, and the citric acid cycle.
In the electron transport chain, high energy electrons are transferred by carrier molecules along a protein chain; this process sets up an electrochemical gradient that drives ATP synthesis
Fermentation occurs when there is no oxygen in respiration

Photosynthesis

The process that plants use to produce food
Photosynthesis occurs in chloroplasts
CO2, water and light are the reactants; O2 and glucose are the products

Enzymes

Biological catalysts
Accelerate chemical reactions by lowering the activation energy required for a reaction.
A suitable substrate molecule binds to the enzyme at its active site.
The reaction occurs, then the enzyme allows the product to detach from the active site, where it can bind a new substrate.

The Nervous System and Hormone Regulation

Receptors detect an environmental stimulus
Nerve impulses carry information along neurons
Nerve impulses involve a change in electrical potential across a nerve cell membrane
Hormones are chemical messengers released into the bloodstream influencing specific target tissues

Other

Homeostasis the maintenance of internal conditions within a tolerable range
Negative feedback mechanisms regulate homeostasis
Positive feedback causes a change to be amplified further (e.g., childbirth, blood clotting)

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Description

Test your knowledge on the molecular geometry of methane (CH4) and the characteristics of isotopes. This quiz covers key concepts including bond angles, electronegativity, and the applications of radioisotopes. Perfect for students aiming to solidify their understanding of basic chemistry principles.