The atom is the smallest unit of an element that keeps the chemical identity of that element.
Missing Word
atom
An atom is the basic building block of an element; splitting it would no longer leave that element. Atoms combine to form molecules and compounds.
Category: Early Atomic Theory
Question 2
In the early 1800s, the English scientist John Dalton proposed that matter is made of tiny, indivisible atoms that combine in whole-number ratios.
Missing Word
Dalton
John Dalton's atomic theory explained the laws of definite and multiple proportions and conservation of matter. Later discoveries of subatomic particles showed atoms are in fact divisible.
Category: Early Atomic Theory
Question 3
The negatively charged subatomic particle found outside the nucleus is the electron.
Missing Word
electron
The electron has a charge of 1- and a very small mass. Electrons occupy the space around the nucleus and take part in chemical bonding.
Category: Atomic Structure
Question 4
The nucleus of ordinary hydrogen, hydrogen-1, consists of just one proton, a particle with a charge of 1+.
Missing Word
proton
The proton carries a charge of 1+ and a mass of about 1 amu. The number of protons in the nucleus is the atomic number, which identifies the element.
Category: Atomic Structure
Question 5
The British physicist James Chadwick discovered the neutron in 1932.
Missing Word
Chadwick
Chadwick identified the neutral particle in the nucleus, which accounted for the extra mass of atoms beyond their protons. Its lack of charge made it harder to detect than the electron or proton.
Category: Atomic Structure
Question 6
Atoms of the same element that contain different numbers of neutrons are called isotopes.
Missing Word
isotopes
Isotopes share an atomic number but differ in mass number, as carbon-12 and carbon-14 do. They have nearly identical chemical behavior because they have the same number of protons and electrons.
Category: Atomic Structure
Question 7
Charged particles formed when atoms gain or lose electrons are called ions.
Missing Word
ions
An ion has unequal numbers of protons and electrons, giving it a net charge. Losing electrons forms a positive ion and gaining electrons forms a negative one.
Category: Atomic Structure
Question 8
A particle that carries a negative charge because it has more electrons than protons is an anion.
Missing Word
anion
An anion forms when an atom or group of atoms gains electrons, as chlorine does to become Cl-. Nonmetals typically form anions.
Category: Atomic Structure
Question 9
A group of two or more atoms bonded tightly enough to behave as a single unit, as in O2, is a molecule.
Missing Word
molecule
A molecule can contain atoms of one element, like O2, or of several elements, like H2O. Molecular formulas give the exact number of each atom in one molecule.
Category: Chemical Formulas
Question 10
On the table that organizes the elements by atomic number, each horizontal row is called a period.
Missing Word
period
A period is a horizontal row of the periodic table, and properties change gradually across it. Vertical columns are called groups.
Category: The Periodic Table
Question 11
Elements that are shiny, malleable and good conductors of heat and electricity are classified as metals.
Missing Word
metals
Metals make up most of the periodic table and lie mostly to the left of the stair-step line. Nonmetals are generally dull and poor conductors.
Category: The Periodic Table
Question 12
Ammonium, with the formula NH4+, is a common polyatomic cation.
Missing Word
Ammonium
The ammonium ion contains one nitrogen and four hydrogen atoms bonded together with an overall 1+ charge. It forms ionic compounds such as ammonium chloride, NH4Cl.
Category: Chemical Nomenclature
Question 13
The polyatomic ion OH-, which carries a 1- charge, is called the hydroxide ion.
Missing Word
hydroxide
Hydroxide is made of one oxygen and one hydrogen atom carrying a 1- charge. It appears in ionic compounds such as sodium hydroxide, NaOH.
Category: Chemical Nomenclature
Question 14
Ionic compounds that contain a fixed number of water molecules within their crystals, such as blue copper(II) sulfate crystals, are called hydrates.
Missing Word
hydrates
A hydrate holds a specific number of water molecules per formula unit, shown with a prefix such as penta- in its name. Heating drives off the water and leaves the anhydrous compound.
Category: Chemical Nomenclature
Question 15
A compound such as HCl that releases H+ when it dissolves in water is an acid.
Missing Word
acid
An acid produces hydrogen ions in water. Acids are named by special rules, such as hydrochloric acid for HCl dissolved in water.
Category: Chemical Nomenclature