Chem Ch 2

Electron's charge

-1.602E-9 Coulombs.

Monatomic Ion

A cation or anion derived from a single atom.

Mass Spectrometry

A method for measuring the relative masses and abundances of atomic-scale particles and molecules very precisely.

Mixture

A mixture consists of two or more substances (elements and/or compounds) that are physically intermingled. Because a mixture is not a substance, in contrast to a compounds, the components of a mixture can vary in their parts by mass. On the atomic scale, a mixture consists of the individual units that make up its component elements and/or compounds. A mixture retains many of the properties of its compounds. Mixtures can be separated into their components by physical changes.

Molecular Formula

A molecular formula uses element symbols and, often, numerical subscripts to give the actual number of atoms of each element in a molecule of the compounds.

Anion

A negatively charged ion.

Covalent Bond

A pair of electrons mutually attracted by the nuclei.

Cation

A positively charged ion.

Structural Formula

A structural formula shows the relative placement and connections of atoms in the molecule. It uses symbols for the atoms and either a pair of dots or a line to show the electron pairs in bonds between atoms.

Metals

About three-quarters of the elements are metals. They are generally shiny solids at room temperature that conduct heat and electricity well. Metal atoms transfer electrons to the nonmetal atoms.

Atoms

All matter consists of atoms, tiny indivisible particles of an element that cannot be created or destroyed. Atoms of one element cannot be converted into atoms of another element. In chemical reactions, the atoms of the original substances recombine to form different substances. Atoms of an element are identical in mass and other properties and are different from atoms of any other element. Compounds result from the chemical combination of a specific ratio of atoms of different elements.

Space-Filling Model

An accurately scaled-up image of the molecule, but bonds are not shown, and it can be difficult to see each atom in a complex molecule.

Nucleus

An atom is mostly space occupied by electrons. In the center is a tiny region called the nucleus that contains all the positive charge (protons) and essentially all the mass of the atom. Neutrons also reside in the nucleus.

Atom

An electrically neutral, spherical entity composed of a positively charged nucleus surrounded by one or more negatively charged electrons. The electrons move rapidly within the available volume, held there by the attraction of the nucleus. An atom's diameter (about 1E-10 m) is about 20,000 times the diameter of its nucleus (5E-15 m). The nucleus contributes 99.97% of the atom's mass, occupies only about 1 quadrillionth of its volume, and is incredibly dense: about 10^14 g/mL. An atom is neutral because the number of protons in the nucleus equals the number of electrons surrounding the nucleus.

Oxoanions

An element, usually nonmetal, is bonded to one or more oxygen atoms.

Molecule

An independent structure of two or more atoms bound together.

Neutron

An uncharge dense particle that resides in the nucleus.

Atomic Mass

Atomic weight; the average of the masses of its naturally occurring isotopes weighted according to their abundance.

Isotopes

Atoms within an element that have different numbers of neutrons and therefore different mass numbers. All isotopes of an element have nearly identical chemical behavior, even though they have different masses.

Binary Acid

Binary acid solutions form when certain gaseous compounds dissolve in water.

Ions

Charged particles that form when an atom (or small group of atoms) gains or loses one or more electrons.

Polyatomic Ions

Consist of two or more atoms bonded covalently and have a net positive or negative charge.

Compound

Consists of two or more different elements that are bonded chemically. The elements are present in fixed parts by mass. This is so because each unit of the compound consists of a fixed number of atoms of each element. Its properties are different from the properties of its component elements. A compound can be broken down into simple substances- its component elements- by chemical change.

Covalent Compounds

Covalent compounds form when elements share electrons, which usually occurs between nonmetals.

Chemical Formula

Element symbols and, often, numerical subscripts show the type and number of each atom in the smallest unit of the substance.

Metals lose electrons

Elements in Group 1A(1) lose one electron, elements in Group 2A(2) lose two, and aluminum in Group 3A(13) loses three.

Nonmetals gain electrons

Elements in Group 7A(17) gain one electron, oxygen and sulfur in Group 6A(16) gain two, and nitrogen in Group 5A(15) gains three.

Naming Binary Ionic Compounds

For all binary ionic compounds, the name of the cation is the name of the metal, and the name of the anion has the suffix -ide added to the root of the name of the nonmetal.

Naming Ionic Compounds

For all ionic compounds, names and formulas give the positive ion (cation) first and the negative ion (anion) second.

Homogenous Mixture

Has no visible boundaries because the components are individual atoms, ions, or molecules. Thus, its composition is uniform.

Heterogeneous Mixture

Has one or more visible boundaries between the components. Thus, its compositions is not uniform, but rather varies from one region to another.

Periods

Horizontal rows. Each period has a number 1-7. Elements in periods have different chemical properties.

Law of Multiple Proportions

If elements A and B react to form two compounds, the different masses of B that combine with a fixed mass of A can be expressed as a ratio of small whole numbers. In two compounds of the same elements, the mass fraction of one element relative to the other element changes in increments based on ratios of small whole numbers. Atomic Theory: Atoms of an element have the same mass and are indivisible. The masses of element B that combine with a fixed mass of element A give a small, whole-number ratio because different numbers of B atoms combine with each A atom in different compounds.

Hydrates

Ionic compounds called hydrates have a specific number of water molecules in each formula unit, which is shown after a centered dot in the formula and noted in the name by a Greek numerical prefix before the word hydrate.

Formula Mass

Ionic compounds don't consist of molecules, so the mass of a formula unit is termed the formula mass instead of molecular mass. To calculate the formula mass of a compound with a polyatomic ion, the number of atoms of each element inside the parentheses is multiplied by the subscript outside the parentheses.

Substance

Matter whose composition is fixed.

Molecular Mass

Molecular weigh; equal to the sum of atomic masses.

Covalent Substances

Most covalent substances consist of molecules. Covalent bonding involves the mutual attraction between two positively charged nuclei and two negatively charged electrons that reside between them.

Law of Definite (or constant) Composition

No matter what its source, a particular compound is composed of the same elements in the same parts (fractions) by mass. Atomic Theory: A compound is a combination of a specific ratio of different atoms, each of which has a particular mass. Thus, each element in a compound constitutes a fixed fraction of the total mass.

Number of neutrons

Number of neutrons = mass number - atomic number.

Periodic Table of the Elements

Organizing scheme for the elements.

Proton

Positive particle.

Cathode Rays

Rays that originate at the negative electrode (cathode) and move to the positive electrode (anode). Cathode rays consist of negatively charged particles found in all matter known as electrons.

Covalent Bonds

Sharing electrons between atoms of different elements.

Ball-and-Stick Model

Shows atoms as balls and bonds as sticks, and the angles between the bonds are accurate.

Oxoacid

Similar to those of the oxyanions, except for suffix change: -ate to - ic and -ite to - ous.

Binary Ionic Compound

Simplest type of ionic compound, one composed of two elements; typically forms when a metal reacts with a nonmetal. Each metal atom loses one or more electrons and becomes a cation, a positively charged ion. Each nonmetal atom gains one or more of the electrons lost by the metal atom and becomes an anion, a negatively charged ion.

Aqueos Solutions

Solutions in water.

Atomic Number (Z)

The atomic number of an element equals the number of protons in the nucleus of each of its atoms. All atoms of an element have the same atomic number, and the atomic of each element is different from that of any other element. All carbon atoms (Z=6) have 6 protons, all oxygen atoms (Z=8) have 8 protons, and all uranium atoms (Z=92) have 92 protons.

Atomic Symbol

The element symbol based on its English, Latin, or Greek name.

Coulomb's Law

The energy of attraction (or repulsion) between two particles is directly proportional to the product of the charges and inversely proportional to the distance between them. Ions with higher charges attract (or repel) each mother more strongly than ions with lower chargers. Smaller ions attract (or repel) each other more strongly than larger ions, because their charges are closer together.

Chemical Bonds

The forces that hold the atoms together in a compound.

Percent by Mass (mass percent, mass %)

The fraction by mass expressed as a percentage (multiplied by 100).

-ic

The ion with the higher charge.

-ous

The ion with the lower charge.

Isotopic Mass

The mass (in amu) of an isotope relative to the mass of carbon-12.

Atomic Mass Unit (amu)

The mass of an atom is measured relative to the mass of an atomic standard. Also known as a dalton (Da). The modern standard is the carbon-12 atom, whose mass is defined as exactly 12 atomic mass units.

Fraction by Mass (mass fraction)

The part of the compound's mass that each element contributes. The mass fraction is fixed no matter what the size of the sample.

Mixtures vs. Compounds

The proportions of the components can vary. The individual properties of the components are observable. The components can be separated by physical means.

Formula Unit

The relative number of cations and anions in an ionic compound. The compound has zero net charge, so the positive charges of the cations balance the negative charges of the anions.

Alkanes

The simplest type of hydrocarbon.

Element

The simplest type of matter with unique physical and chemical properties. It consists of only one kind of atom and, therefore, cannot be broken down into a simpler type of matter by any physical or chemical methods. Each element is unique because the properties of its atoms are unique.

Hydrocarbons

The simplest type of organic compound, containing only carbon and hydrogen.

Law of Mass Conservation

The total mass of substances does not change during a chemical reaction. The number of substances may change and, by definition, their properties must, but the total amount of matter remains constant. Matter cannot be created or destroyed. Atomic Theory: Atoms cannot be created or destroyed or converted into other types of atoms. Therefore, a chemical reaction, in which atoms are combined differently, cannot possibly result in a mass change.

Mass Number (A)

The total number of protons and neutrons in the nucleus of an atom. Each proton and each neutron contributes one unit to the mass number.

Ionic Substances

There are no molecules in an ionic compound. Ionic bonding involves the mutual attraction among positive and negative ions.

Nonmetals

They are generally gases or dull, brittle solids at room temperature and conduct heat and electricity poorly.

Ionic Compounds

Transferring electrons from one element to another. All ionic compounds are solid arrays of oppositely charged ions. Ionic compounds are neutral because they contain equal numbers of positive and negative charges.

Binary Covalent Compounds

Typically formed by the combination of two nonmetals. The element with the lower group number in the periodic table comes first in the name. The element with the higher group number comes second and is named with its root and the suffix -ide. When the compound contains oxygen and any of the halogens chlorine, bromine, or iodine, the halogen is named first. If both elements are in the same group, the one with the higher period number is named first.

Organic Compounds

Typically have complex structures that consist of chains, branches, and/or rings of carbon atoms bonded to hydrogen atoms and, often, to atoms of oxygen, nitrogen, and a few other elements.

Groups

Vertical rows. Each group has a number 1-8 and either the letter A or B. Chemicals in groups have similar chemical properties.