Chemistry Chapter 2 Quiz

Chemical Context of Life

• Matter is anything that takes up space and has mass.
• Matter is composed of elements.
• Elements are substances that cannot be broken down into other substances by chemical reactions.
• There are 92 naturally occurring elements.
• Elements are represented by symbols (e.g., Gold (Au), copper (Cu), carbon (C)).
• Elements can exist in three physical states: solid, liquid, and gas.
• Substances whose molecules are arranged in regular, repeating patterns are solids
• Molecules in liquids flow easily around one another. Liquids assume the shape of their containers
• Molecules in gases fly in all directions at great speeds
• The plasma state of matter occurs at very high temperatures, where atoms lose their electrons.
• Compounds are substances composed of two or more elements in a fixed ratio.
• A compound always has a specific ratio of atoms of different elements. (e.g., water (H₂O), sodium chloride (NaCl)).
• Essential elements are required by all living organisms for normal cellular functions.
• Essential elements make up ~20-25% and 96% of all living matter.
• These elements include oxygen (O), carbon (C), hydrogen (H) and nitrogen (N).
• The elements calcium (Ca), phosphorus (P), potassium (K), and sulfur (S) make up ~3.5% .
• Trace elements are required by all living organisms for normal cellular functions in very small quantities
• Examples: Iron (Fe), Iodine (I), Zinc (Zn)

Atoms

• Atoms are the smallest units of matter that retain the properties of an element.
• An atom contains subatomic particles: neutrons (no charge), protons (positive charge), and electrons (negative charge).
• The nucleus of an atom tightly packs protons and neutrons
• Protons determine the atomic number.
• Electrons rapidly move around the nucleus
• Atomic mass is determined by protons and neutrons.
• Atomic mass unit (amu) is also known as Dalton.
• Electrons have a much smaller mass than protons or neutrons.

Isotopes

• Atoms of the same element can have different numbers of neutrons.
• These are called isotopes.
• Isotopes have the same atomic number but different mass numbers.
• Most naturally occurring elements exist as mixtures of isotopes.
• Carbon, for example, has three isotopes: carbon-12, carbon-13, carbon-14.
• Carbon-12 is stable, while carbon-13 and carbon-14 are unstable. Carbon-14 is radioactive.
• The atomic mass of an element is the weighted average mass of all the naturally occurring isotopes of that element.
• Radioactive isotopes undergo spontaneous decay, releasing particles and energy.

Atomic Number and Mass Number

• The atomic number of an element is the number of protons in the nucleus of an atom of that element. (e.g., Helium - 2).
• Different isotopes of an element will have a different mass number due to the number of neutrons present.
• Mass number = number of protons + number of neutrons.

Electron Shells

• Electrons occupy specific energy levels or shells.
• Electrons farther from the nucleus have higher energy levels.
• The first electron shell holds a maximum of 2 electrons. (1s)
• The second electron shell holds a maximum of 8 electrons. (2s, 2p).
• The third shell holds a maximum of 18 electrons.
• Electrons tend to exist in the lowest available states of potential energy.

Valence Shell

• The valence shell is the outermost electron shell of an atom.
• Valence electrons are the electrons present in the outermost electron shell.
• The number of valence electrons determines the chemical behavior of the atom.
• Atoms with the same number of valence electrons show similar chemical behavior.

Inert Elements

• Inert elements are chemically unreactive elements that have completely filled valence electron shells.
• Example: Helium, Neon, Argon, Krypton, Xenon, and Radon.

Electron Orbitals

• Electron orbitals describe the space where an electron is found 90% of the time.
• Unlike electron shells, orbital depicts complex, 3D shapes of electron distribution in space
• An electron can exist in different orbitals of the same energy level.

Chemical Bonding

• Chemical bonds are interactions between atoms in order to form chemical compounds
• Covalent bonds are formed when atoms share valence electrons. This results in molecules.
• Ionic bonds are formed when one atom loses one or more electrons and another atom gains them. This results in ions that attract to each other.
• Hydrogen bonds form when a hydrogen atom covalently bonded to a highly electronegative atom (such as oxygen or nitrogen) is attracted to another electronegative atom or molecule.
• Van der Waals forces are very weak attractions between molecules that are close together.

Chemical Reactions

• Chemical reactions involve changing the composition of a substance by making or breaking chemical bonds, where reactant materials change into product materials.
• Reactants are the materials that start the chemical reaction, while products are the result of the chemical reaction.
• Coefficients show the quantity of each molecule involved.
• The number of atoms in reactants must equal the number of atoms in the products and the overall charged need to be equal. This reflects the law of conservation of mass.