Chemistry Flashcards
Element
a substance composed of only one type of atom
Molecule
a unit composed of two or more atoms joined together by chemical bonds
Compound
a substance composed of 2 or more elements that have been joined by chemical bonds
Mixture
a combination of 2 or more substances that do NOT chemically bond
Ionic Bonds
- atoms sometimes strip electrons from their bonding partners
- an example is the transfer of an electron from sodium to chlorine
- after the transfer of an electron, both atoms have charges
- a charged atom for molecules is called an ion
- an ionic bond is an attraction between an anion(-) and a cation(+) - oppositely charged ions
Ions and Ionic Compounds
- When at atom or molecule loses electrons, it becomes positively charged
- positively charged ions are called cations
- when an atom molecule gains electrons, it becomes negatively charged
- negatively charged ions are called anions
- an atom or molecule can lose more than one electron
- when molecules loose electrons, polyatomic ions are formed
Ionic Compounds
- compounds formed by ionic bonds are called ionic compounds
- salts, such as sodium chloride are often found in nature as crystals
Covalent Bonds
- molecules are formed by covalent bonds
- a covalent bond is when two atoms share one or more parts of outer-shell electrons
- in a covalent bond, the shared electron counts as part of each atom’s valence shell
- much stronger than ionic bonds - holds lots of energy
- a single covalent bond or double bond is sharing of two parts of valence electrons
- covalent bonds can form between atoms of the same element of atoms of different elements
Electronegativity
- outer orbital determines reactivity of atom - electronegativity
- electronegativity is an atom’s attraction for the electrons in a covalent bond
- the more electronegativity an atom, the more strongly it pulls shared electrons toward itself
Polar Covalent Bond
- in a nonpolar covalent bond, the atoms share the electron equally
- in a polar covalent bond, one atom is more electronegative and the atoms do not share the electron equally
The structure of water
Its two hydrogen atoms are joined to one oxygen atom by single covalent bonds.
But the electrons of the covalent bonds are not shared equally between oxygen and hydrogen.
This unequal sharing makes water a polar molecule.
Weak Chemical Bonds
- most of the strongest bonds in organisms are covalent bonds that form a cell’s molecules
- weak chemical bonds, such as ionic bonds and hydrogen bonds, are also important
- weak chemical bonds reinforce shapes of large molecules and help molecules adhere to each other.
2 types of compounds exist in living things
inorganic and organic compounds
Inorganic Compounds
Water - living things consists of 60% to 90% water, which acts as a way for transport and chemical activities within the cell
Salts - they are important for maintaining osmotic balance in the cell and for many of the cells chemical reactions
acids and bases - these compounds are important for maintaining the proper balance of acidity and alkalinity in the cell
Organic Compounds
- all organic compounds contain the elements carbon and hydrogen
- larger than inorganic compounds
Elements in Organisms
- the most frequently occurring chemical elements in living things are carbon, hydrogen, and oxygen
- however, a variety of other elements are needed by living organisms these include: sulfer, calcium, phosphorus, iron and sodium
Role of elements
sulfer- essential element in variable group of amino acids
calcium- is necessary for bone and tooth formation, blood clotting, and nerve impulse transmission
phosphorus- is also used for bone and tooth formation, essential element in nucleotides, including ATP
iron- is a part of hemoglobin, a molecule needed to carry oxygen in the blood
Sodium- balances both water in the body and acid/base concentration. It also functions in nerve function
General Properties of Aqueous Solutions
Acids- substances to ionize in solution to form hydrogen and increase the concentration of H+ in the solution
Bases- are substances that can react with or accept H+ ions.
Salts- are ionic compounds that can be formed by replacing one or more of the hydrogen ions of an acid by a different positive ion
Acids, Bases and pH
- dissociation of water molecules leads to acidic and basic conditions that affect living organisms
- water dissociates into hydronium ions and hydroxide ions
- charges in the concentration of these ions can have a great affect on living organisms
Acid- a chemical compound that dissociates into one or more hydrogen ions and one or more negative ions. An acid donates H+ ions to solutions.
Base- dissociates into one or more positive ions and one or more hydroxide ions. A base accepts H+ ions and removes them from solution, reducing the hydrogen ion concentration of a solution
Strong and Weak Acids
- strong acids ionize or dissociates completely in water
- weak acids ionize slightly (less than 5%) in water
pH
- to describe the activity of a solution we use the pH scale
- is a measure of the concentration of H+ ions in a solution
- is determined by the relative concentration of H+
pH Scale
- a logarithmic scale used to express the amount of H+ ions in a solution
- pH is determined as the negative log of the (H+) of a solution
- a change of one whole number represents a tenfold change in the number of H+ ions
- a solution with pH 3 has ten times as many H+ ions as a solution with pH 4
Buffers
- a buffer is a substance that helps minimize the change in the pH of a solution when acids or bases are added
- consist of acid-base pair that reversibly combines with hydrogen ions
- buffers work by releasing H+ when their concentration falls, and absorbing H+ when their concentration rises
- are important to living organisms because most cells can survive and function normally only within a relatively narrow range
