Ch.2: Basic Chemistry Flashcards
Matter
• Anything that occupies space and has mass
• Matter may exist as one of three states:
*Solid: definite shape and volume
*Liquid: definite volume; shape of container
*Gaseous: neither a definite shape nor volume
Matter may be changed:
- Physically
* Chemically
Physically changed matter
- Changes do not alter the basic nature of a substance
* Examples include changes in the state of matter (solid, liquid, or gas)
Chemically changed matter
Changes alter the chemical composition of a substance
Energy
- The ability to do work
* Has no mass and does not take up space
Kinetic energy
Energy is doing work
Potential energy
Energy is inactive or stored
Forms of energy:
- Chemical energy is stored in chemical bonds of substances
- Electrical energy results from movement of charged particles
- Mechanical energy is energy directly involved in moving matter
- Radiant energy travels in waves; energy of the electromagnetic spectrum
Energy form conversions
ATP (adenosine triphosphate) traps the chemical energy of food in its bonds
Elements
Fundamental units of matter
96 percent of the body is made from four elements:
- Oxygen (O)—most common; 65% of the body’s mass
- Carbon (C)
- Hydrogen (H)
- Nitrogen (N)
Atoms
- Building blocks of elements
- Atoms of elements differ from one another
- Atomic symbol is chemical shorthand for each element
What are the charges of the basic subatomic particles?
- Protons (p+) are positively charged
- Neutrons (n0) are uncharged or neutral
- Electrons (e−) are negatively charged
Number of protons equals:
- Number of electrons in an atom
* Positive and negative charges cancel each other out
Ions
Atoms that have lost or gained electrons
Electrons determine an atom’s:
Chemical behavior and bonding properties
To identify an element, we need to know the:
- Atomic number
- Atomic mass number
- Atomic weight
Atomic number
- Equal to the number of protons that the atom contains
- Unique to atoms of a particular element
- Indirectly tells the number of electrons in an atom
Atomic mass number
Sum of the protons and neutrons contained in an atom’s nucleus
Atomic weight
Approximately equal to the mass number of the element’s most abundant isotope
Isotopes
- Atoms that have the same number of protons and electrons but vary in the number of neutrons
- Isotopes have the same atomic number but different atomic masses
Radioisotope
- Heavy isotope of certain atoms
- Tends to be unstable
- Decomposes to more stable isotope
Radioactivity
- Process of spontaneous atomic decay
* Used to tag and trace biological molecules through the body
Molecule
Two or more atoms of the same elements combined chemically
Compound
Two or more atoms of different elements combined chemically to form a molecule of a compound
Chemical reactions occur when:
Atoms combine with or dissociate from other atoms
Chemical bonds
Energy relationships involving interactions among the electrons of reacting atoms
Electrons occupy energy levels called:
Electron shells (or energy levels)
Electrons closest to the nucleus are most strongly attracted to its:
Positive charge
Distant electrons further from the nucleus are likely to interact with:
Other atoms
How to fill the atom’s electrons shells:
- Shell 1 can hold a maximum of 2 electrons
- Shell 2 can hold a maximum of 8 electrons
- Shell 3 can hold a maximum of 18 electrons
- Subsequent shells can hold more electrons
Bonding involves interactions only between electrons in:
- The outermost (valence) shell
* Atoms with full valence shells do not form bonds
Rule of eights
- The key to chemical reactivity
- Atoms are considered stable when their outermost (valence) shell has 8 electrons
- Atoms with 8 electrons in the valence shell are considered stable and chemically inactive (inert)
- The exception to this rule of eights is shell 1, which can hold only 2 electrons
Reactive elements
- Atoms will gain, lose, or share electrons to complete their outermost orbitals when fewer than 8 electrons are in the valence shell
- Chemical bonding helps atoms achieve a stable valence shell
Ionic bonds
- Form when electrons are completely transferred from one atom to another
- Allow atoms to achieve stability through the transfer of electrons
Ions
Result from the loss or gain of electrons
• Anions have negative charge due to gain of electron(s)
• Cations have positive charge due to loss of electron(s)
Tend to stay close together because opposite charges attract
Covalent bonds
- Atoms become stable through shared electrons
- Electrons are shared in pairs
- Single covalent bonds share one pair of electrons
- Double covalent bonds share two pairs of electrons
- Can be described as either nonpolar or polar
Nonpolar covalent bonds
- Electrons are shared equally between the atoms of the molecule
- Electrically neutral as a molecule
- Example: carbon dioxide
Polar covalent bonds
- Electrons are not shared equally between the atoms of the molecule
- Molecule has a positive and negative side, or pole
- Example: water