Chapter 2: The Components of Matter

Merged flashcards from Chapter 2 of Chemistry: The Molecular Nature of Matter and Change.

Substance

Matter with a fixed composition; includes:

• Elements (the simplest type of matter with one type of atom)

• Compounds (two or more different elements that are bonded chemically)

Element

The simplest type of matter with unique physical and chemical properties

• Has only one kind of atom

• Visible properties are unique due to submicroscopic differences

• Some exist as molecules, like oxygen as O₂

Molecule

An independent structure of two or more atoms bound together

Atom

The smallest unit of an element that retains its chemical nature

Compound

Two or more different elements that are bonded chemically

Defined by:

1. A fixed mass ratio of each element per unit

2. Properties different from that of the individual elements

3. Changes possible through chemical reactions

Fixed mass ratio

Property of compounds where elements are present in fixed parts by mass

Mixtures

Two or more substances that are physically intermingled, but not chemically combined; some properties include:

1. Potential variation in mass parts

2. Component-level retention

3. The ability to be separated by physical processes

Hetrogenous mixtures

Mixtures with one more visible boundaries among the components

• Variation is distributed from one region to another

• Boundaries may only be seen with microscopes at times

Homogenous mixtures (solutions)

Mixtures with no visible boundaries

• Uniform composition and uniformly intermingled (not attached)

• Cannot visually tell whether homogenous or an element or compound

Filtration

The separation of a mixture based on particle size, used to separate solids from liquids

Crystallization

Based on solubility; impure solids can be dissolved and then reconstituted through this

Solubility

Of a substance, the amount that dissolves in a fixed volume of solvent at a given temperature

Distillation

Based on volatility, where:

1. In simple types, more volatile contents are vaporized first and collected

2. In fractional types, many steps are used to separate components with small differences, like with petroleum

Volatility

The tendency of a substance to become a gas

Chromatography

Also based on solubility; components flow through a solid or viscous liquid called a stationary phase with the lowest soluble elements moving faster

Mass laws

Includes:

1. The law of mass conservation

2. The law of definite composition

3. The law of multiple proportions

Law of mass conservation

States that the total mass of substances does not change during a chemical reaction

• The number of substances may change, but the total amount of matter (or energy that results) remains constant overall

Composition calculation

A fixed proportion of elements remain a compound, either via:

1. Fraction by mass (mass fraction), calculating the part of the compound’s mass that each element contributes

2. Percent by mass (mass percent), expressing fraction by mass as a percentage

These should equal 1 part (100%) and can be compared to determine substance similarity via the law of definite composition

Law of definite composition

States that no matter what its source, a particular compound is composed of the same elements in the same parts by mass

• Mass percents, for example, can be used to find the mass of each substance

Law of multiple proportions

States that 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

• For example, in:

  • CO (57.1% oxygen, 42.9% carbon), and

  • CO₂ (72.7% oxygen, 27.3% carbon),

  • taking ((72.7% / 27.3%) / (57.1% / 42.9%)) = (2.66 / 1.33) = 2,

• signifying that there is twice as much oxygen in the second carbon compound, made possible by their composition of whole atoms

  • The mass ratio of carbon to oxygen in CO₂ is 2 times the mass ratio of carbon to oxygen in CO.

John Dalton

Scientist who presented the atomic theory of matter, which stated that all matter consists of indivisible, unchangeable atoms of fixed, unique mass

• These help explain the mass laws

Electric charge

While it was known this existed, scientists for many years did not understand their composition, only their effects

Cathode rays

Observed as part of an experiment to investigate current; with a light-sensitive phosphor coated end, a ray could be seen when the electric power source was turned on

• When a charged plate or magnetic force was applied, the rays deflected towards positive sides, thus demonstrating their negative charge

• Gave way to naming of electrons, as it was recognized that these particles are found in all matter

Coulomb (C)

The SI unit of electrical charge

Charge-mass ratio

Ratio found in 1897 by J. J. Thomson stating that the electron was about 2000 times lighter than hydrogen via a cathode ray tube, giving off -1.76 × 10⁸ coulombs per gram

• Went against theorem that atoms could contain smaller particles

Charge

Discovered via Robert Millikan’s oil drop experiment, where charged oil droplets falling in between two variably electrically-charged plates allowed him to measure this based on their rate of fall, giving -1.602 × 10^-19 coulombs

• This was then used to solve for mass using the charge/mass ratio, giving 9.10 × 10^-28 grams

Plum-pudding model

Model proposed by J. J. Thomson for a spherical, positively-charged sphere of mater with electrons embedded within it to attain neutrality

• Tested by Ernst Rutherford by firing alpha particles at a gold foil, expecting straight-pass through with this model

• Actually found that atoms deflected the particles, thus reasoning something small and dense in the atoms was the cause — the nucleus

Nucleus

Discovered by Ernst Rutherford after his gold-foil experiment, concluding that an atom was mostly space occupied by electrons and a tiny nucleus region with all the positive charge of the atom

• Also proposed existence of positively-charged protons

• Later modified in 1932 by James Chadwick, who discovered the neutral neutron here

Atom

An electrically neutral, spherical entity composed of a positively charged central nucleus, surrounded by one or more negatively charged electrons

Electron

A rapidly-moving, negatively-charged particle held by the attraction of the nucleus

• 2000 times smaller in terms of mass than a proton or neutron, but the same in number as protons to maintain neutrality

Nucleus

Protons and neutrons in the center of the atom

• Very small; diameter is 20,000 times smaller than the total diameter

• Contributes 99.97% of the mass, but only 1 quadrillionth of the volume, creating high density (10¹⁴ g/mL)

Proton

A particle within the nucleus with a positive charge

• Has the same magnitude of charge of an electron, but with the opposite sign

• This always equals the number of electrons

Neutron

A particle in the nucleus with no charge; these are neutral

Mass number (A)

The total number of protons and neutrons in the nucleus of an atom, can be used for simple isotope names

• Written as a left superscript, like ¹²C (carbon-12)

Atomic number (Z)

The number of protons in the nucleus of each of an element’s atoms

• Equals the number of electrons

• Stays consistent across isotopes

• Written as a left subscript: ₆C signifies 6 protons (and by extension 6 electrons)

Neutron count (N)

This changes across isotopes

• Found by subtracting the constant atomic number (Z) from the mass number (A)

Atomic symbol

A one or two letter abbreviation for the English, Latin, or Greek name of an element

Isotopes

Atoms of an element that have different numbers of neutrons and therefore different mass numbers

• These have nearly-identical chemical behavior, even with different masses, due to electrons

Atomic mass unit (amu)

1/12 of the mass of a carbon-12 atom; based on relative mass

• Also known as the dalton (Da)

• About 1.66054 × 10²⁴ grams

Mass spectrometry

A method for measuring the relative masses and abundances of atomic-scale particles

• Electrons collide with an atom’s electron to produce a particle with one positive charge, which are then attracted towards negatively-charged plates and eventually strike a detector to record positions and abundances based on deflection amounts through a magnet

• This provides the isotopic mass for each individual isotope, allowing for a later calculation of the atomic mass

Atomic mass

The weighted average of naturally occurring isotopes according to their abundances; these can sometimes change overtime with ranges provided

Dmitri Mendeleev

Russian scientist who, in 1871, arranged elements by increasing atomic mass and chemical properties to form the periodic table of elements

Periodic table of elements

Table based on work by Mendeleev, arranged by atomic number

• Arranged in periods (rows) and groups (columns)

  • Each period has a number from 1 to 7; each group has a number from 1 to 18

Group

A column on the periodic table; elements here usually have the same outer electron configuration and thus similar chemical behavior

• Numbered from 1 to 18; includes:

  • 1: alkali metals

  • 2: alkaline earth metals

  • 3 to 12: transition elements

  • 13 to 16: named for first element in group

  • 17: halogens

  • 18: noble gases

• Also called a “family” for elements

Main-group elements

This includes groups 1, 2, and 13 through 18, with predictable outer charges

Transition elements (transition metals)

These include groups 3 through 12

Inner transition elements

Includes the lanthanides and actinides between groups 3 and 4

Alkali metals

The name for group 1, except for hydrogen

• Classified as reactive metals

Alkaline earth metals

The name for group 2

• Classified as reactive metals

Halogens

The name for group 17

• Classified as reactive nonmetals

Noble gases

The name for group 18

• Classified as relatively unreactive nonmetals due to their full valence shells

Element classifications

Can be grouped into three:

• Metals

• Nonmetals

• Metalloids

  • Marked by a staircase line from boron to tellurium (but not aluminum)

Metals

Group of elements located in the left and middle portions of the periodic table

• Includes many main-group elements and all transition elements

• Shiny and solid at room temperature

• Can conduct heat and electricity

• Malleable and ductile

Metalloids (semimetals)

Group of elements located along the staircase line of the periodic table

• Includes boron to tellurium, except aluminum

• Shiny and solid, but brittle

• Semiconductors of heat and electricity

• Has properties of both metals and nonmetals

Nonmetals

Group of elements located in the upper-right portion of the periodic table; includes hydrogen as well

• Includes some of the main-group elements

• Gases or dull, brittle solids at room temperature

• Poor conductors

• Not malleable or ductile

Natural elements

These typically occur as compounds combined with other elements, with some exceptions:

• Noble gases occur as separate atoms

• N and O occur as two atoms, and S occurs as 8 atoms

• C occurs as nearly pure deposits of coal

• Cu, Ag, Au, and Pt are sometimes uncombined

Otherwise, elements combine through electron interactions in ionic (transferring electron) or covalent (sharing electron) bonds

Ionic compound

A compound that forms when electrons are transferred instead of shared between ions, creating a cation and anion who lose and gain electrons respectively and create a neutral overall force

• Elements in these tend to form ions with the same number of electrons as in an atom of the nearest noble gas

Binary ionic compound

The simplest type of ionic compound, typically between a metal and nonmetal, resulting in a three-dimensional array

Cation

An atom that loses one or more electrons, becoming positively charged

• Written as a positive superscript, like Mg²⁺

Anion

An atom that gains one or more electrons, becoming negatively charged

• Written as a negative superscript, like Cl^-

Covalent bond

Bond where elements (typically nonmetals) share electrons

• Can be seen in the simple case of hydrogen gas (H₂), which share an electron with each other as they are drawn to the other atom’s nucleus at an optimal distance

Polyatomic ion

Two or more atoms bonded covalently with a net positive or negative charge

• Seen in many ionic compounds, where the overall unit requires the transfer of electrons to attain a more stable state

Chemical formula

A notation of atomic symbols and numerical subscripts that shows the type and number of each atom in a molecule or formula unit of a substance

Ionic compound names

These give the name of the cation first and anion second

Zinc and cadmium (Zn and Cd)

These form a 2+ charge despite being transition metals

Silver (Ag)

This forms a 1+ charge despite being a transition metal

Add Roman numerals to the name, without spaces.

How do I name transition metals with more than one charge variant, like in CuS?

Polyatomic ions

Groups of atoms that form a charged unit for pairing with other ions

Name the full polyatomic ion, with no -ide suffix.

How do I name polyatomic ions in an ionic compound, like Na₂CO₃?

Ammonium and hydronium (NH₄⁺ and H₃O⁺)

The most common polyatomic ions that serve as cations

Add a parentheses and subscript to denote the number of polyatomic ion units needed.

How do I write a compound requiring two or more polyatomic ions, like iron(III) sulfate?

Oxoanions

Polyatomic anions composed of a central (usually nonmetal) element bonded to oxygen atoms, named according to the number of oxygens present

• Families always have the same charge

Oxoanion naming rules

• -ate for more O atoms

• -ite for less O atoms

• per- and hypo- for halogens with one more and one less, respectively

Hydrates

Ionic compound with a specific number of water molecules, retaining the base name but adding a prefix + “hydrate” at the end

Acids

Hydrogen-containing compounds, formed as anions with an H⁺ cation

Binary acids

Acids with one nonmetal anion

Oxoacids

Acids with an oxoanion

“Hydro” + root + “ic” acid, for non-oxoanions

How do I name a binary acid like HF? What anions named under this?

Oxoanion root + “-ic” or “-ous” + acid

• “-ic” used if ending in “-ate” (more oxidized)

• “-ous” used if ending in “-ite” (less oxidized)

How do I name an oxoacid, like HClO₄?

Binary covalent compounds

Covalent compounds between two nonmetals

• First nonmetal retains the name

• Second nonmetal retains root + “ide”

• Add prefixes for all but 1 in the first nonmetal

• Determine order by examining which has a halogen and oxygen, then lowest group, then highest period

How do I name a binary covalent compound, like N₂O?

Straight-chain alkanes

The simplest alkane type with no branches, named for the number of C atoms in the chain and the suffix “-ane”

• Follow the general formula C_nH_2n+2

• First four roots:

  • Methane

  • Ethane

  • Propane

  • Butane

Hydrocarbons

The simplest type of organic compound, alkanes are a simple type of this

Organic compound

A compound that consists of chains, branches, or rings of carbon atoms bonded to hydrogen atoms; hydrocarbons are a simple type of this

Formula unit

The relative numbers of cations and anions in an ionic compound’s array instead an individual molecule

Use the designated prefix for the number of C atoms + “-ane”.

How do I name a straight-chain alkane?

Take the sum of the atomic masses, multiplying those within a polyatomic ion group accordingly.

How do I calculate the molecular or formula mass of a compound, like Ba(NO₃)₂?

Molecular formula

A formula that denotes the actual number of atoms of each element in a molecule of the compound

• Seen with H₂O, with two H atoms and one O atom in each molecule

Structural formula

A formula that denotes the relative placements and connections in a molecule

• Seen with (H—O—H) or (H:O:H)

Ball-and-stick model

A model that shows atoms as balls and bonds as sticks to convey the measure of angles but exaggerates sizes and distances

Space-filling model

A model that shows the relative sizes, distances, and angles between atoms but may obscure bonds and other atoms

Macromolecule

An extremely large molecule, like DNA