Chapter 2 Flashcards
Matter
Is anything that takes up space and has mass.
Is made up of elements.
Element
Is a substance that cannot be broken down to other substances by chemical reactions.
Compound
Is a substance consisting of two or more different elements combined in a fixed ratio.
A compound has characteristics different from those of its elements, meaning it often has emergent properties.
Mass
The amount of matter in an object.
Essential Elements
An organism needs essential elements to live a healthy life and reproduce. They are similar among organisms, but there is some variation.
For example, humans need 25 elements, but plants need only 17.
Four elements that make up 96% of living matter
Oxygen (O)
Carbon (C)
Hydrogen (H)
Nitrogen (N)
Trace elements
Are required by an organism in only minute quantities.
Atom
Is the smallest unit of matter that still retains the properties of an element.
Subatomic particles
Compose an atom. There are more than a hundred types of subatomic particles, however these are important for now: Neutrons, protons, electrons.
Proton
Has one unit of positive charge
Electron
Has one unit of negative charge.
Neutron
Is electrically neutral.
Atomic Nucleus
The dense core at the center of an atom. Protons and neutrons are packed together tightly in the atomic nucleus. Electrons are rapidly moving around the nucleus, and it is the attraction between opposite charges that keeps the electrons in the vicinity of the nucleus.
Dalton
Unit of measurement used for subatomic particles, atoms, and molecules.
Equal to about 1.7 x 10^-24 gram.
Same as the atomic mass unit (amu)
Mass of neutrons and protons
Close to 1 dalton.
Mass of electron
About 1/2,000 of a neutron or proton.
Atomic number
Number of protons, unique to each element.
Mass number
The sum of protons plus neutrons in the nucleus of an atom.
Atomic mass
The total mass of an atom
Isotopes
Atoms with more neutrons than other atoms of the same element.
Decay
A process where the nucleus has a tendency to lose subatomic particles.
Radioactive isotope
An isotope in which the nucleus decays spontaneously, giving off particles and energy. When the radioactive decay leads to a change in the number of protons, it transforms the atom to an atom of a different element.
Half-life
The time it takes for 50% of the parent isotope to decay.
Energy
The capacity to cause change, for instance, by doing work.
Potential energy
The energy that matter possesses because of its location or structure.
An electron’s potential energy is determined by…
Its energy level
How can an electron move from one shell to another?
By absorbing or losing an amount of energy equal to the difference in potential energy between its position in the old shell and that in the new shell.
When an electron loses energy:
It “falls back” to a shell closer to the nucleus, and the lost energy is usually released to the environment as heat.
The chemical behavior of an atom is determined by:
The distribution of electrons in the atom’s electron shells. Depends mostly on the number of electrons in its outermost shell.
How is the periodic table arranged?
The elements are arranged in rows, or periods, corresponding to the number of electron shells in their atoms. The left-to-right sequence of elements in each row corresponds to the sequential addition of electrons and protons.
First electron shell:
Holds 2 electrons. Is the lowest available state of potential energy for electrons (all matter tends to exist in the lowest available state of potential energy).
Valence electrons
Outer electrons
Valence shell
The outermost electron shell
Elements are inert when…
They have full valence shells.
Orbital
The three-dimensional space where an electron is found 90% of the time.
1s orbital
One spherical orbital in the first electron shell.
2s orbital
Larger spherical orbital on the second shell
2p orbitals
Three dumbbell-shaped orbitals on the second shell that move along the x, y, and z axes.
Chemical bonds
An attraction between two atoms, resulting from a sharing of outer-shell electrons or the presence of opposite charges on the atoms. The bonded atoms gain complete outer electron shells.
Covalent bond
The sharing of a pair of valence electrons by two atoms.
Molecule
Two or more atoms held together by covalent bonds
Single bond
A pair of shared electrons.
Double bond
Two pairs of shared valence electrons.
Valence
The bonding capacity of the atom. Usually equals the number of unpaired electrons required to complete the atom’s valence shell.
Electronegativity
The attraction of a particular atom for the electrons of a covalent bond.
Nonpolar covalent bond
The electrons are shared equally because the two atoms have the same electronegativity.
Polar covalent bond
The electrons of the bond are not shared equally. This results in a partial negative charge and a partial positive charge.
Ion
A charged molecule or atom.
Cation
A positively charged ion.
Anion
A negatively charged ion.
Ionic bond
An attraction between cations and anions (because of their opposite charges).
Ionic compounds
AKA salts. Compounds formed by ionic bonds.
Hydrogen Bond
The attraction between a hydrogen and an electronegative atom.
van der Waals interactions
Weak attractions between molecules or parts of molecules that result from transient local partial charges.
What determines a molecules shape?
They are determined by the positions of the atom’s orbitals.
Hybridization of orbitals in 2s and 2p orbitals
Form four teardrop-shaped hybrid orbitals. Called a tetrahedron.
What does molecular shape determine?
It determines how biological molecules recognize and respond to one another with specificity.
Chemical reactions
The making and breaking of chemical bonds that leads to changes in the composition of matter.
Matter is conserved in a chemical reaction because…
Reactions cannot create or destroy atoms but can only rearrange the electrons among them.
All chemical reactions are reversible
True
The greater the concentration of reactant molecules,
The more frequently they collide with one another and have an opportunity to react and form products.
Chemical Equilibrium
The point at which the reactions offset one another exactly
