From Dalton’s first ideas to the periodic table. Discover the vocabulary of the tiny particles that make up everything around us.
These terms were extracted from Chemistry by OpenStax, eCampusOntario (© 2016 Rice University; adapted by BCcampus) which is licensed under a Creative Commons Attribution 4.0 International License.
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set of postulates that established the fundamental properties of atoms
Here are the postulates of Dalton’s atomic theory.
(also, law of definite proportions) all samples of a pure compound contain the same elements in the same proportions by mass
This statement is known as the law of definite proportions or the law of constant composition.
(also, law of constant composition) all samples of a pure compound contain the same elements in the same proportions by mass
This statement is known as the law of definite proportions or the law of constant composition.
when two elements react to form more than one compound, a fixed mass of one element will react with masses of the other element in a ratio of small whole numbers
This small, whole-number ratio supports the law of multiple proportions.
positively charged particle consisting of two protons and two neutrons
Adjust the slit width to produce a narrower or broader beam of α particles to see how that affects the scattering pattern.
negatively charged, subatomic particle of relatively low mass located outside the nucleus
The term “electron” was coined in 1891 by Irish physicist George Stoney, from “electric ion.”
atoms that contain the same number of protons but different numbers of neutrons
Another important finding was the discovery of isotopes.
uncharged, subatomic particle located in the nucleus
The nucleus contains the majority of an atom’s mass because protons and neutrons are much heavier than electrons, whereas electrons occupy almost all of an atom’s volume.
massive, positively charged center of an atom made up of protons and neutrons
A small, relatively heavy, positively charged body, the nucleus, must be at the center of each atom.
positively charged, subatomic particle located in the nucleus
The nucleus contains the majority of an atom’s mass because protons and neutrons are much heavier than electrons, whereas electrons occupy almost all of an atom’s volume.
negatively charged atom or molecule (contains more electrons than protons)
An atom that gains one or more electrons will exhibit a negative charge and is called an anion.
average mass of atoms of an element, expressed in amu
However, a more detailed analysis showed that mesothorium was chemically identical to radium (another decay product), despite having a different atomic mass.
(also, unified atomic mass unit, u, or Dalton, Da) unit of mass equal to 1/12 of the mass of a ¹²C atom
When describing the properties of tiny objects such as atoms, we use appropriately small units of measure, such as the atomic mass unit (amu) and the fundamental unit of charge (e).
number of protons in the nucleus of an atom
The number of protons in the nucleus of an atom is its atomic number (Z).
positively charged atom or molecule (contains fewer electrons than protons)
Positively charged atoms called cations are formed when an atom loses one or more electrons.
one-, two-, or three-letter abbreviation used to represent an element or its atoms
Chemical symbols are used to represent atoms and elements.
alternative unit equivalent to the atomic mass unit
First published in 1807, many of Dalton’s hypotheses about the microscopic features of matter are still valid in modern atomic theory.
(also called the elementary charge) equals the magnitude of the charge of an electron (e) with e = 1.602 × 10⁻¹⁹ C
When describing the properties of tiny objects such as atoms, we use appropriately small units of measure, such as the atomic mass unit (amu) and the fundamental unit of charge (e).
electrically charged atom or molecule (contains unequal numbers of protons and electrons)
The term “electron” was coined in 1891 by Irish physicist George Stoney, from “electric ion.”
sum of the numbers of neutrons and protons in the nucleus of an atom
The total number of protons and neutrons in an atom is called its mass number (A).
alternative unit equivalent to the atomic mass unit
(The Dalton (Da) and the unified atomic mass unit (u) are alternative units that are equivalent to the amu.)
formula showing the composition of a compound given as the simplest whole-number ratio of atoms
For example, titanium dioxide (used as pigment in white paint and in the thick, white, blocking type of sunscreen) has an empirical formula of TiO₂.
compounds with the same chemical formula but different structures
Acetic acid and methyl formate are examples of isomers—compounds with the same chemical formula but different molecular structures (Figure 8).
formula indicating the composition of a molecule of a compound and giving the actual number of atoms of each element in a molecule of the compound.
A molecular formula is a representation of a molecule that uses chemical symbols to indicate the types of atoms followed by subscripts to show the number of atoms of each type in the molecule.
compounds in which the relative orientations of the atoms in space differ
There are also various types of spatial isomers, in which the relative orientations of the atoms in space can be different.
shows the atoms in a molecule and how they are connected
The structural formula for a compound gives the same information as its molecular formula (the types and numbers of atoms in the molecule) but also shows how the atoms are connected in the molecule.
one of two substances that have the same molecular formula but different physical and chemical properties because their atoms are bonded differently
Acetic acid and methyl formate are structural isomers, compounds in which the molecules differ in how the atoms are connected to each other.
inner transition metal in the bottom of the bottom two rows of the periodic table
And inner transition metals in the two rows at the bottom of the table (the top-row elements are called lanthanides and the bottom-row elements are actinides.
element in group 1
These elements (except hydrogen) are known as alkali metals, and they all have similar chemical properties.
element in group 2
An alkaline earth metal (group 2) loses two electrons and forms a cation with a 2+ charge, and so on.
element in group 16
Other groups with specific names are the pnictogens (group 15), chalcogens (group 16), halogens (group 17), and the noble gases (group 18, also known as inert gases).
vertical column of the periodic table
A modern periodic table arranges the elements in increasing order of their atomic numbers and groups atoms with similar properties in the same vertical column (Figure 2).
element in group 17
Other groups with specific names are the pnictogens (group 15), chalcogens (group 16), halogens (group 17), and the noble gases (group 18, also known as inert gases).
(also, noble gas) element in group 18
Other groups with specific names are the pnictogens (group 15), chalcogens (group 16), halogens (group 17), and the noble gases (group 18, also known as inert gases).
(also, lanthanide or actinide) element in the bottom two rows; if in the first row, also called lanthanide, or if in the second row, also called actinide
And inner transition metals in the two rows at the bottom of the table (the top-row elements are called lanthanides and the bottom-row elements are actinides.
inner transition metal in the top of the bottom two rows of the periodic table
And inner transition metals in the two rows at the bottom of the table (the top-row elements are called lanthanides and the bottom-row elements are actinides.
(also, representative element) element in columns 1, 2, and 12–18
Moving from the far left to the right on the periodic table, main-group elements tend to form cations with a charge equal to the group number.
element that is shiny, malleable, good conductor of heat and electricity
This apparatus consisted of a sealed glass tube from which almost all the air had been removed; the tube contained two metal electrodes.
element that conducts heat and electricity moderately well, and possesses some properties of metals and some properties of nonmetals
And metalloids (elements that conduct heat and electricity moderately well, and possess some properties of metals and some properties of nonmetals—shaded purple).
(also, inert gas) element in group 18
A meteorite found in central Indiana contains traces of the noble gas neon picked up from the solar wind during the meteorite’s trip through the solar system.
element that appears dull, poor conductor of heat and electricity
When atoms of nonmetal elements form ions, they generally gain enough electrons to give them the same number of electrons as an atom of the next noble gas in the periodic table.
(also, series) horizontal row of the periodic table
The elements are arranged in seven horizontal rows, called periods or series, and 18 vertical columns, called groups.
properties of the elements are periodic function of their atomic numbers.
The modern statement of this relationship, the periodic law, is as follows: the properties of the elements are periodic functions of their atomic numbers.
table of the elements that places elements with similar chemical properties close together
We will also introduce one of the most powerful tools for organizing chemical knowledge: the periodic table.
element in group 15
Other groups with specific names are the pnictogens (group 15), chalcogens (group 16), halogens (group 17), and the noble gases (group 18, also known as inert gases).
(also, main-group element) element in columns 1, 2, and 12–18
The elements can also be classified into the main-group elements (or representative elements) in the columns labeled 1, 2, and 13–18.
(also, period) horizontal row of the period table
The elements are arranged in seven horizontal rows, called periods or series, and 18 vertical columns, called groups.
element in columns 3–11
In fact, transition metals and some other metals often exhibit variable charges that are not predictable by their location in the table.
attractive force between the nuclei of a molecule’s atoms and pairs of electrons between the atoms
When electrons are “shared” and molecules form, covalent bonds result.
(also, molecular compound) composed of molecules formed by atoms of two or more different elements
These molecular compounds (covalent compounds) result when atoms share, rather than transfer (gain or lose), electrons.
electrostatic forces of attraction between the oppositely charged ions of an ionic compound
When electrons are transferred and ions form, ionic bonds result.
compound composed of cations and anions combined in ratios, yielding an electrically neutral substance
Magnesium and nitrogen react to form an ionic compound.
(also, covalent compound) composed of molecules formed by atoms of two or more different elements
For example, sodium chloride melts at 801 °C and boils at 1413 °C. (As a comparison, the molecular compound water melts at 0 °C and boils at 100 °C.)
ion composed of a single atom
The ions that we have discussed so far are called monatomic ions, that is, they are ions formed from only one atom.
polyatomic anion composed of a central atom bonded to oxygen atoms
Oxyanions are polyatomic ions that contain one or more oxygen atoms.
ion composed of more than one atom
Some of the more important polyatomic ions are listed in Table 6.
compound that contains hydrogen and one other element, bonded in a way that imparts acidic properties to the compound (ability to release H⁺ ions when dissolved in water)
Hydrogen chloride dissolved in water is a binary acid called hydrochloric acid.
compound containing two different elements.
The name of a binary compound containing monatomic ions consists of the name of the cation (the name of the metal) followed by the name of the anion (the name of the nonmetallic element with its ending replaced by the suffix –ide).
system of rules for naming objects of interest
This will be covered in more detail in the next module on nomenclature.
compound that contains hydrogen, oxygen, and one other element, bonded in a way that imparts acidic properties to the compound (ability to release H⁺ ions when dissolved in water)
Typical oxyacids consist of hydrogen combined with a polyatomic, oxygen-containing ion.