RP

Atoms, Molecules, and Chemical Bonds

Matter

  • Matter is anything that occupies space and has mass

  • Matter is composed of chemical elements

  • Elements are substances that cannot be broken down into other substances


Chemical Elements Required for Life

  • There are 92 naturally occurring elements on Earth

  • 25 elements are essential for life

  • O, C, H, N are most abundant


Atoms

  • Each element consists of one kind of atom

  • An atom is the smallest unit of matter that still retains the properties of an element


Atomic Structure

  • Atoms are composed of subatomic particles

  • Protons are positively charged & has mass

  • Neutrons are electrically neutral & has mass

  • Electrons are negatively charged, has no discernable mass


Atomic Number and Atomic Mass

  • Elements differ in the number of subatomic particles in their atoms

  • Atomic number: the number of protons, determining which element it is

  • Mass number: the sum of both protons and neutrons


Electron Arrangement

  • Electrons orbit atoms at specific distances called electron shells

  • The first inner shell can hold up to two electrons

  • All subsequent outer shells can hold up to eight electrons

  • Atoms with incomplete outer electron shells are reactive


Chemical Reactions

  • Chemical reactions enable atoms to give up or acquire electrons to complete their outer shells

  • These reactions result in atoms joining together with other atoms, forming molecules

  • Atoms are held together in molecules by chemical bonds


Covalent Bonds

  • A covalent bond forms when two atoms share outer-shell electrons

  • The number of covalent bonds an atom can form is equal to the number of electrons needed to fill its outer shell

  • When electrons are shared evenly between atoms, they form a non-polar covalent bond


A double covalent bond results from sharing two pairs of electrons.

Chemical Reactions (1)

  • Cells constantly change molecules by breaking existing chemical bonds and forming new ones

  • Chemical reactions do not create or destroy; they only rearrange it


Water

  • Water, which covers 75% of Earth’s surface and makes up between 70% and 95% of a cell’s volume, is a polar molecule that forms hydrogen bonds

  • Polar molecules are the result of polar covalent bonds, in which electrons are not shared equally between atoms


Hydrogen Bonds

  • The polarity of water results in electrical attractions between neighboring water molecules

  • These attractions are called hydrogen bonds


Properties of Water

  • Water is solvent

  1. Due to its polarity, water facilities chemical reactions, both outside and within living systems

  2. It dissolves many chemical substances

  3. A solution contains dissolved substances, which are then called solutes

  4. Hydrophilic molecules attract water

  5. Hydrophobic molecules do not attract water


Water is involved in Creating and Breaking Chemical Bonds

  • The structure of water results in essential properties for life

  • Water is involved in joining together monomers, and breaking apart polymers

  • Monomers: repeated subunit of many large, organic molecules

  • Polymers: Large organic molecules formed by


Dehydration Synthesis and Hydrolysis

  • Cells use common reactions to build or degrade polymers

  • In a dehydration reaction, an -OH and -H are removed as a water molecule when monomers are joined to build polymers

  • In a hydrolysis reaction, components of water are added when polymers are broken down