Chapter 2 Atoms and Molecules

Question 1

Element

Answer 1

A chemical element (or element) is a chemical substance consisting of atoms having the same number of protons in their atomic nuclei (i.e. the same atomic number, Z).[1] There are 118 elements that have been identified, of which the first 98 occur naturally on Earth with the remaining 20 being Synthetic elements.

Question 2

Chemical symbol

Answer 2

In chemistry, a symbol is a code for a chemical element. It is usually derived from the name of the element, often in Latin.

Question 3

Atom

Answer 3

An atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element. Every solid, liquid, gas, and plasma is made up of neutral or ionized atoms.

Question 4

Matter

Answer 4

The substance or substances of which any physical object consists or is composed:

Question 5

Electron

Answer 5

The electron is a subatomic particle, symbol e− or β−, with a negative elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have no known components or substructure.

Question 6

Proton

Answer 6

The proton is a subatomic particle, symbol p or p+, with a positive electric charge of +1e elementary charge and mass slightly less than that of a neutron. Protons and neutrons, each with mass approximately one atomic mass unit, are collectively referred to as “nucleons”.

Question 7

Neutron

Answer 7

The neutron is a subatomic particle, symbol n or n0, with no net electric charge and a mass slightly larger than that of a proton. Protons and neutrons, each with mass approximately one atomic mass unit, constitute the nucleus of an atom, and they are collectively referred to as nucleons.

Question 8

Atomic nucleus

Answer 8

Almost all of the mass in an atom is made up from the protons and neutrons in the nucleus with a very small contribution from the orbiting electrons. Neutrons have no charge and protons are positively charged. Because the nucleus is only made up of protons and neutrons it is positively charged

Question 9

Atomic number

Answer 9

Atomic number is the number of protons, and therefore also the total positive charge, in the atomic nucleus.

Question 10

Periodic Table

Answer 10

A table of the chemical elements arranged in order of atomic number, usually in rows, so that elements with similar atomic structure (and hence similar chemical properties) appear in vertical columns.

Question 11

Electron configuration

Answer 11

In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals.

Question 12

Atomic mass unit

Answer 12

The unified atomic mass unit (symbol: u) or dalton (symbol: Da) is the standard unit that is used for indicating mass on an atomic or molecular scale (atomic mass). One unified atomic mass unit is approximately the mass of one nucleon (either a single proton or neutron) and is equivalent to 1 g/mol.

Question 13

Atomic mass

Answer 13

For atoms, the protons and neutrons of the nucleus account for almost all of the mass, and the atomic mass measured in u has nearly the same value as the mass number.

Question 14

Isotopes

Answer 14

A mixture of atoms with different number of neutrons and thus different masses.

Question 15

Radioisotopes

Answer 15

Radioisotopes are radioactive isotopes of an element. Different isotopes of the same element have the same number of protons in their atomic nuclei but differing numbers of neutrons. They can also be defined as atoms that contain an unstable combination of neutrons and protons.

Question 16

Autoradiography

Answer 16

An autoradiograph is an image on an x-ray film or nuclear emulsion produced by the pattern of decay emissions (e.g., beta particles or gamma rays) from a distribution of a radioactive substance.

Question 17

Orbital

Answer 17

An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom.

Question 18

Principal energy level

Answer 18

The principal quantum number tells us the main energy level or shell of an electron, and gives us an idea of the electron density around the nucleus. It also tells us the number of nodes, how many subshells there are and the maximum number of electrons for each shell.

Question 19

Electron shell

Answer 19

An electron shell is the outside part of an atom around the atomic nucleus. It is a group of atomic orbitals with the same value of the principal quantum number n. Electron shells have one or more electron subshells, or sublevels.

Question 20

Valence shell

Answer 20

The valence shell is the outermost shell of an atom. It is usually (and misleadingly) said that the electrons in this shell make up its valence electrons, that is, the electrons that determine how the atom behaves in chemical reactions.

Question 21

Valence electrons

Answer 21

The valence electrons (VE) are the electrons in the outer shell of an atom. The valence electrons are the ones involved in forming bonds to adjacent atoms. Therefore, the number of VE is important for determining the number of bonds an atom will form, the number of unpaired electrons, and an atom’s formal charge.

Question 22

Compound

Answer 22

A compound is a molecule made of atoms from different elements. All compounds are molecules, but not all molecules are compounds. Hydrogen gas (H2) is a molecule, but not a compound because it is made of only one element.

Question 23

Molecule

Answer 23

A molecule is the smallest particle in a chemical element or compound that has the chemical properties of that element or compound. Molecules are made up of atom s that are held together by chemical bonds. These bonds form as a result of the sharing or exchange of electron s among atoms.

Question 24

Chemical formula

Answer 24

A chemical formula is a way of expressing information about the proportions of atoms that constitute a particular chemical compound, using a single line of chemical element symbols, numbers, and sometimes also other symbols, such as parentheses, dashes, brackets, commas and plus (+) and minus (−) signs.

Question 25

Empirical formula

Answer 25

The empirical formula is the simplest formula for a compound. A molecular formula is the same as or a multiple of the empirical formula, and is based on the actual number of atoms of each type in the compound. For example, if the empirical formula of a compound is C3H8 , its molecular formula may be C3H8 , C6H16 , etc.

Question 26

Molecular formula

Answer 26

A molecular formula is the same as or a multiple of the empirical formula, and is based on the actual number of atoms of each type in the compound. For example, if the empirical formula of a compound is C3H8 , its molecular formula may be C3H8 , C6H16 , etc.

Question 27

Structural formula

Answer 27

The structural formula of a chemical compound is a graphic representation of the molecular structure, showing how the atoms are arranged. The chemical bonding within the molecule is also shown, either explicitly or implicitly.

Question 28

Mole

Answer 28

It is defined as the amount of any chemical substance that contains as many elementary entities, e.g., atoms, molecules, ions, or electrons, as there are atoms in 12 grams of pure carbon-12 (12C), the isotope of carbon with relative atomic mass 12 by definition.

Question 29

Avogadro’s number

Answer 29

In chemistry and physics, the Avogadro constant (symbols: L, NA) is the number of constituent particles, usually atoms or molecules, that are contained in the amount of substance given by one mole. Thus it is the proportionality factor that relates the molar mass of a material to its mass. 6.02*10^23

Question 30

Reactants

Answer 30

The reactants are the substances that are present before the chemical change takes place. They are the things that are present at the starting point. By convention, the chemical symbols for the reactants are written on the left hand side of the chemical reaction equation.

Question 31

Product

Answer 31

Are the substances that are formed during the chemical change. They are the things that are present at the end. By convention, the chemical symbols for the products are written on the right hand side of the chemical reaction equation.

Question 32

Coefficients

Answer 32

The coefficients give the number of molecules (or atoms) involved in the reaction. In the example reaction, two molecules of hydrogen react with one molecule of oxygen and produce two molecules of water.

Question 33

Dynamic equilibrium

Answer 33

A dynamic equilibrium exists once a reversible reaction ceases to change its ratio of reactants/products, but substances move between the chemicals at an equal rate, meaning there is no net change. It is a particular example of a system in a steady state.

Question 34

Chemical bonds

Answer 34

A chemical bond is an attraction between atoms that allows the formation of chemical substances that contain two or more atoms.

Question 35

Bond energy

Answer 35

It is the heat required to break one mole of molecules into their individual atoms.

Question 36

Covalent bond

Answer 36

A covalent bond is a chemical bond that involves the sharing of electron pairs between atoms.

Question 37

Covalent compounds

Answer 37

A covalent compound is made when two or more nonmetal atoms bond by sharing valence electrons.

Question 38

Single covalent bond

Answer 38

A single covalent bond is when only one pair of electrons is shared between atoms.

Question 39

Double covalent bond

Answer 39

A double covalent bond is where two pairs of electrons are shared between the atoms rather than just one pair. Some simple molecules containing double bonds.

Question 40

Triple covalent bond

Answer 40

A triple bond in chemistry is a chemical bond between two atoms involving six bonding electrons instead of the usual two in a covalent single bond. The most common triple bond, that between two carbon atoms, can be found in alkynes.