Terms in this set (37)
Classification of Materials Observing, describing, Classifying and using
materials (a macroscopic view).
* The material(s) of which an object is composed
- Heterogeneous mixtures - Homogeneous mixtures
• Pure substances:elements and compounds
• Names and formulae of substances
• Metals, semimetals and nonmetals
• Electrical conductors, semiconductors and insulators • Thermal conductors and insulators
• Magnetic and nonmagnetic materials
What matter is
* Atoms and molecules (simple and giant)
* Material structures and properities: Linking macroscopic properties of
materials to micro(particle) structure
* Intermolecular and intramolecular forces (chemical bonds). Physical state and density explained in terms of these forces. Particle kinetic energy and temperature. (NOTE TO SELF: (some is covered already but not all))
In Atomic combination,
Molecular structure and
A chemical bond as the net electrostatic force between two atoms sharing electron
Oxidation number of atoms in molecules to explain their relative 'richness' in electrons.
Molecular shapes predicted using the valence shell electron pair repulsion (VSEPR theory)
A substance formed by the combination of elements in fixed proportions. The formation of a compound involves a chemical reaction: i.e. there is a change in the configuration of the valence electrons of the atoms. Compounds, unlike mixtures, cannot be separated by physical means.
are substance that cannot be decomposed into simpler substances. In an element, all the atoms have the same number of protons or electrons although the number of neutrons may vary. There are 92 naturally occurring elements.
A system of two or more distinct chemical substances. Homogeneous mixtures are those in which the atoms or molecules are interspersed, as in a mixture of gases or in a solution. Heterogeneous mixtures have distinguishable phases, e.g. a mixture of iron filings and sulphur. In a mixture there is no redistribution of valence electrons, and the components retain their individual chemical properties. Unlike compounds, mixtures can be separated by physical means (distillation, crystallization, etc.
the chemical properties of an element are determined by the charge of its atomic nucleus, i.e. by the number of protons. This number is called the atomic num- ber and is denoted by the letter Z . The mass of an atom depends on how many nucleons its nucleus contains. The number of nucleons, i.e. the total number of protons plus neutrons, is called the atomic mass number and is denoted by the letter A.
A change in which one or more chemical elements or compounds (the reactant) form new compounds (the products). All reactions are to some extent reversible; i.e., the products can also react to give the original reactants. However, in many cases the extent of this back reaction is negligibly small, and the reaction is regarded as irreversible. Biology - Any change in behavior of an organism in response to a stimulus.
completely transferred from one atom to another. In the process of either losing or gaining negatively charged electrons, the reacting atoms form ions. The oppositely charged ions are attracted to each other by electrostatic forces, which are the basis of the ionic bond.
For example, during the reaction of sodium with chlorine:
sodium (on the left) loses its one valence electron to chlorine (on the right),
resulting in ↓
a positively charged sodium ion (left) and a negatively charged chlorine ion (right).
A homogenous mixture of a liquid (the solvent) with a gas or solid (the solute). In a solution, the molecules of the solute are discrete and mixed with the molecules of solvent. There is usually some interaction between the solvent and solute molecules. Two liquids that can mix on the molecular level are said to be miscible. In this case, the solvent is the major component and the solute the minor component.
Ionic compounds share
many features in common:
Ionic bonds form between metals and nonmetals.
In naming simple ionic compounds, the metal is always first, the nonmetal second (e.g., sodium chloride).
Ionic compounds dissolve easily in water and other polar solvents.
In solution, ionic compounds easily conduct electricity. * Ionic compounds tend to form crystalline solids with high melting temperatures.
The relative proportions in which elements form compounds or in which substances react.
The second major type of atomic bonding occurs when atoms share electrons. As opposed to ionic bonding in which a complete transfer of electrons occurs, covalent bonding occurs when two (or more) elements share electrons. Covalent bonding occurs because the atoms in the compound have a similar tendency for electrons (generally to gain electrons). This most commonly occurs when two nonmetals bond together. Because both of the nonmetals will want to gain electrons, the elements involved will share electrons in an effort to fill their valence shells. A good example of a covalent bond is that which occurs between two hydrogen atoms. Atoms of hydrogen (H) have one valence electron in their first electron shell. Since the capacity of this shell is two electrons, each hydrogen atom will "want" to pick up a second electron. In an effort to pick up a second electron, hydrogen atoms will react with nearby hydrogen (H) atoms to form the compound H2. Because the hydrogen compound is a combination of equally matched atoms, the atoms will share each other's single electron, forming one covalent bond. In this way, both atoms share the stability of a full valence shell.
Titration of volumetric analysis in which a volume of one reagent (the titrant) is added to a known volume of another reagent slowly from a burette until an end point is reached. The volume added before the end point is reached is noted. If one of the solutions has a known concentration, that of the other can be calculated.
every pair of electrons shared between two atoms, a single covalent bond is formed. Some atoms can share multiple pairs of electrons, forming multiple covalent bonds. For example, oxygen (which has six valence electrons) needs two electrons to complete its valence shell. When two oxygen atoms form the compound O2, they share two pairs of electrons, forming two covalent bonds.
A known pH point of an acid and base interaction as shown by a chemical indicator change in color.
Are the shorthand to represent the valence electrons of an atom. The structures are written as the element symbol surrounded by dots that represent the valence electrons. The Lewis structures for the elements in the first two periods of the periodic table are shown below.
A logarithmic scale (from 1 (acid) to 14 (base)) for expressing the acidity or alkalinity of a solution. To a first approximation, the pH of a solution can be defined as -log 10 c, where c is the concentration of hydrogen ions in moles per cubic decimeter. A pH of below 7 indicates an acid solution; one above 7 indicates alkaline solution. More accurately, the pH depends not on the concentration of hydrogen ions but on their activity, which can not be measured experimentally. pH stands for 'potential of hydrogen'. The scale was introduced by S.P. Sorensen in 1909.
Polar and non polar
There are, in fact, two subtypes of covalent bonds. The H2 molecule is a good example of the first type of covalent bond, the nonpolar bond. Because both atoms in the H2 molecule have an equal attraction (or affinity) for electrons, the bonding electrons are equally shared by the two atoms, and a nonpolar covalent bond is formed. Whenever two atoms of the same element bond together, a nonpolar bond
There are in fact two
subtype of covalent bonds
The H2 molecule is a good example of the first type of covalent bond, the nonpolar bond. Because both atoms in the H2 molecule have an equal attraction (or affinity) for electrons, the bonding electrons are equally shared by the two atoms, and a nonpolar covalent bond is formed. Whenever two atoms of the same element bond together, a nonpolar bond
* valence electrons in the water molecule spend more time around the oxygen atom than the hydrogen atoms, the oxygen end of the molecule develops a partial negative charge (because of the negative charge on the electrons). For the same reason, the hydrogen end of the molecule develops a partial positive charge. Ions are not formed; however, the molecule develops a partial electrical charge across it called a dipole. The water dipole is represented by the arrow in the pop-up animation (above) in which the head of the arrow points toward the electron dense (negative) end of the dipole and the cross resides near the electron poor (positive) end of the m
* is a partial electrical charge across a molecule. Dipoles exist in polar molecules because one end is electron-dense end the other end is electron-poor.
uneven distribution of electrons.
Chemist Gilbert Lewis
proposed that since elements are most stable when they have eight electrons in their valence shell, atoms with fewer than eight valence electrons bond together to share electrons and complete their valence shells.
Are completely transferred from one atom to another.
However, the electrons in the valence shell determine how atoms bond with each other.
occurs when two nonmetals bond together.
A polar covalent bond
is formed when one atom has a stronger affinity for electrons than the other. This causes the bonding electrons to spend more time around the atom with the stronger affinity.
When two atoms have
an equal attraction
(or affinity) for elections
the bonding electrons are equally shared by the two atoms and a nonpolar covalent bond is formed.
In water molecules
the large oxygen molecule has a stronger affinity for electrons than the small hydrogen atoms. Because oxygen has a stronger pull on the bonding electrons, this leads to unequal sharing and the formation of a polar covalent bond.
Two atoms of the
same elements are:
of the same element bond together, a nonpolar covalent bond is formed.
happens when atoms share electrons.
Two main types of
Are ionic bonding and covalent bonding.
form crystalline solids due their strong intermolecular forces.
form between metals and nonmetals.
* The formation of a chemical bond involves competition for bonding elections occupying valence orbitals.
* If the competing atoms have equal electronegativity, the bonding electrons are shared equally.
* Electron sharing between atoms with high electronegativity results in covalent bonding.
* Electron sharing between atoms with low electronegativity often results in metallic bonding.
* If the competing atoms have unequal electronegativity the result may be unequal covalent bonding; if unequal enough that electrons transfer, the result will be ionic bonding.
* Bonding theory was created by chemists to describe, explain, and predict natural events and observed properties.
* Only the valence electrons of the central atom (s) are important for molecular shape.
* Valence electrons are paired in a molecule or polyatomic ion.
* Bonding pairs of electrons and lone pairs of electrons are treated approximately equally.
* Valence electrons pairs repel each other electronstatically.
* The molecular shape is determined by the position of the electrons pairs when they are a maximum distance apart.