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Chem.200-2.Matter

General Chemistry Ch. 2 - The Components of Matter

QuestionAnswer
Origin of the idea of Atoms Democritus reasoned if you cut matter smaller and smaller, you’ll eventually reach a particle so small that it can no longer be cut. Aristotle disagreed, and because of his greater influence, Democritus’ idea was suppressed for 2000 years.
When was the modern atomic model developed and by who? In the 19th century by John Dalton. He proposed an atomic model that explained mass laws and eventually led to today’s model of an atom.
Element Simplest type of matter with unique physical and chemical properties. An element consists of only ONE type of atom; therefore, it cannot be broken down into a simpler type of matter by any physical or chemical methods.
And element is one kind of _____ Substance
Substance Matter whose composition is fixed.
Molecule, e.g. O2 An independent structure consisting of two or more atoms chemically bound together. O2 is an example of a diatomic molecule: it is a molecule consisting of two atoms
Compound A type of matter composed of two or more different elements that are chemically bound together. Elements are present in fixed parts by mass (fixed mass ratio) & properties are different from its component elements.
Compare and contrast molecules and compounds Molecule = at least two atoms joined together. Compound = a molecule with at least two different elements. All compounds are molecules, but not all molecules are compounds.
Because the composition of compounds are fixed, they are considered _____ Substances
Example of how compounds have different properties than their component elements Sodium is a soft, silvery metal. Chlorine is a yellow-green poisonous gas. Sodium chloride is table salt.
Breaking down a compound into its components is a type of _____ change Chemical
Mixture A group of two or more substances (elements and/or compounds) that are physically intermingled
How does a mixture differ from a compound? In contrast to a compound, the components of a mixture can vary in their parts by mass. A mixture is not a substance because its composition is not fixed. Also: a mixture retains many of the properties of its components.
Are chemical changes needed to separate mixtures just like compounds? No, physical changes can separate mixtures. E.g. boiling salt water can separate the water from the salt.
Law of mass conservation The total mass of substances does not change during a chemical reaction. The number of substances may change and, by definition, their properties must. But total amount of matter remains constant.
Law of definite (or constant) composition No matter what its source, a particular compound is composed of the same elements in the same parts (fractions) by mass.
Fraction by mass (mass fraction) That part of the compound’s mass that each element contributes. It is obtained by dividing the mass of each element by the total mass of the compound. E.g. calcium in calcium carbonate has a mass fraction of 0.4.
The percent by mass (mass %) Is the fraction by mass expressed as a percentage. E.g. calcium in calcium carbonate has a mass % of 40%.
How would you determine the mass of an element in a sample? Take the mass % of the element in the compound (mass element in compound/mass of compound) and multiply it by the mass of compound in the sample.
Law of multiple proportions 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.
What was lacking in Dalton’s model of the atom? The model did not explain why atoms bond as they do: why do two, not three, hydrogen atoms bond with one oxygen atom in water? Charged particles were not accounted for in his model.
Side note: How do neon lights work Inside the glass tube there is a gas like neon, argon, or krypton. At the ends of the tube are electrodes that send out high enough electrical currents to ionize the gas, exciting it so that it emits photons.
Side note: How do fluorescent lights work Similar but instead of using neon, argon, etc. it uses mercury vapor. When ionized it emits UV light (tanning beds). In a building fluorescent lights are coated with phosphor which absorbs the UV light and emits photons.
Cathode; Anode An negatively charged electrode; a positively charged electrode
Atomic nucleus An atomic nucleus consists of protons and neutrons, with the exception being the simplest hydrogen nucleus, which is a single proton.
Charges: Proton, neutron, electron Positive, neutral, negative
Atomic number (Z) Equals the number of protons in the nucleus in each of its atoms.
Of the _____ known elements, _____ occur in nature; the remaining _____ have been synthesized by nuclear scientists 116; 90; 26
Mass number (A) The total number of protons and neutrons in the nucleus of an atom.
Atomic symbol The element’s symbol. E.g. C for carbon, O for oxygen. The atomic number (Z) is written to the left of the atomic symbol as a subscript and the mass number (A) is written to the left as a superscript.
Number of neutrons calculation N = A – Z (neutrons = mass number – atomic number)
All atoms of an element are identical in _____ number but not in _____ number. Why? Atomic number; mass number. Because of isotopes
Isotopes Atoms that have different numbers of neutrons and therefore different mass numbers.
Isotope example: Carbon 98.89% of naturally occurring carbon is Carbon-12 isotope, 1.11% is Carbon-13, and .01% is Carbon-14. Carbon-9, 10, 11, 15, and 16 have been created in labs.
How do different isotopes behave? The chemical properties of an element are primarily determined by the number of electrons, so all isotopes of an element have nearly identical chemical behavior, even though they have different masses.
Atomic mass unit Defined as 1/12th the mass of a carbon-12 atom. Hydrogen has a mass of 1.008amu. Note: the name amu has been changed to Dalton (Da); thus carbon’s mass is 12 daltons
The isotopic makeup of an element is determined by _____ Mass spectrometry
Mass spectrometry A method for measuring the relative masses and abundances of atomic-scale particles very precisely.
Atomic mass of an element The average of the masses of its naturally occurring isotopes weighted according to their abundances
Very brief explanation on how mass spectrometers work They ionize particles and then separate them by mass which will provide the relative abundance of isotopes of elements that exist.
Periodic table of elements Originally developed by Dmitri Mendeleev’s, it is an organizing scheme of the elements, arranged by atomic number.
The elements in the periodic table are ordered left to right by their _____ Atomic number
Periodic table: periods and groups Periods: horizontal rows 1 - 7, groups: vertical columns 1 – 8 and letter A or B
A vs B groups The eight A groups are the main-group, or representative, elements. The ten B groups contain the transition elements.
Lanthanides and actinides Inner transition elements, all metals. They fit between Group 3B(3) and Group 4B(4) and are usually placed below the main body of the table
The “staircase” line that runs from the top of Group 3A(13) to the bottom of Group 6A(16) The diving line between the metals and non-metals. Most of the elements directly along this line are metalloids (AKA semimetals)
Metals About 3/4ths of the elements are metals. They are generally shiny solids at room temperature (mercury is the only liquid metal at room temp) that conduct heat and electricity well and are malleable and ductile.
Nonmetals Appear in the small upper-right portion of the table. They are generally gases or dull, brittle solids at room temperature (bromine is the only liquid) and conduct heat and electricity poorly.
Metalloids (semimetals) Elements that have properties between those of metals and nonmetals. Several metalloids including silicon and germanium play major roles in electronics.
Organic chemistry. Relevant to… Studies the compounds of carbon, specifically those that contain hydrogen and often oxygen, nitrogen, and a few other elements. Relevant to… fuels, drugs, dyes, polymers, etc.
Inorganic chemistry Focuses mainly on compounds of all non-carbon elements. Relevant to: catalysts, electronic materials, metal alloys, mineral salts, etc.
Group 1A(1) consists of the… Excluding hydrogen: alkali metals: Li, Na, K, Rb, Cs, Fr
Group 2A(2) consists of the… Alkaline earth metals: Be, Mg, Ca, Sr, Ba, Ra
Groups 1A(1) and 2A(2) are both… Highly reactive
Group 7A(17) consists of the… Halogens: F, Cl, Br, I, At
Halogens are… Highly reactive nonmetals
Group 8A(18) Noble gasses: He, Ne, Ar, Kr, Xe, Rn
The noble gasses are… Relatively unreactive nonmentals
How are the other groups named, e.g. Group 6A They are generally named for the first element in the group, e.g. group 6A is the oxygen family.
Elements in a group have _____ chemical properties and elements in a period have _____ chemical properties Similar; different
Ionic compounds Transferring electrons from the atoms of one element to those of another to form ionic compounds
Covalent compounds Sharing electrons between atoms of different elements to form covalent compounds
Chemical bonds The forces that hold the atoms of elements together in a compound
Ions Charged particles that form when an atom (or small group of atoms) gains or loses one more electrons.
The simplest type of ionic compound is a _____ Binary ionic compound
Binary ionic compound One composed of just two elements
Binary ionic compounds typically form when A metal reacts with a nonmetal. Each metal atom loses some electrons and becomes a cation. The nonmetal atoms gain the electrons lost by the metal atoms and become anions. Thus electrons are transferred to the nonmetal.
Cation Positively charged ions
Anion Negatively charged ions
After electrons are transferred, how do the atoms form a bond? The resulting cations and anions attract each other through electrostatic forces and form the ionic compound.
All binary ionic compounds are _____ Solids
Monatomic ion A cation or anion derived from a single atom e.g. Na+
Polyatomic ion A cation or anion derived from a small group of atoms. I.e. polyatomic ions consist of two or more atoms bonded covalently and have a net positive or negative charge. e.g. OH-
Why does the atomic arrangement of atoms in sodium chloride appear to form a three dimensional pattern? Because the Na+ cations simultaneously repel each other while attracting the Cl- anions, creating a regular array of alternating Na+ and Cl- ions
The strength of ionic bonding depends on the strength of the attractions and repulsions between charged particles as described by… Coulomb’s law (equation from physics: F = (k*q1*q2)/(d^2)
Coulomb’s law illustrates that Ions with higher charges attract (or repel) each other more strongly than ions with lower charges. Likewise: smaller ions attract each other more strongly than larger ions because their charges are close together.
What is the charge on an ionic compound? There is none. Ionic compounds are neutral; that is, they possess no net charge because they contain equal numbers of positive and negative charges (not necessarily an equal number of positive/negative ions).
Using the periodic table, what rule is used when making predictions about how many electrons an element will lose or gain when forming an ion? General rule: metals lose electrons and nonmetals gain electrons to form ions with the same number of electrons as in an atom of the nearest noble gas
Covalent compounds usually occur between Nonmetals
Covalent bond A pair of electrons mutually attracted by the two nuclei.
Elements that occur as diatomic molecules at room temperature H, N, O, F, Cl, Br, I (e.g. O exists as O2 in the air at room temperature). P is tetratomic, S and Se are octatomic.
Distinction between ionic substances and covalent substances Most covalent substances consist of molecules (e.g. a cup of water consists of water molecules). In contrast, molecules don’t exist in a sample of an ionic compound. Salt is one, continuous array of ions.
Soluble Able to be dissolved, esp. in water. E.g. a soluble compound dissociating
Molecular compound Always involve two nonmentals, e.g. CO, CO2, NH3, etc. As opposed to ionic compounds which involve a metal with a nonmetal
Why does the polyatomic ion ammonium NH4+ have a positive charge N is sharing one electron with each of the 4 H’s, totaling 4 electrons. Since N is in group 5 it should have 5 electrons in its outer shell, the lack of an electron accounts for the positive charge.
Elements of life: Building Blocks H, C, N, O. Over 99% of the atoms in organisms are of these four elements.
Elements of life: Major minerals AKA macronutrients: Na, Mg, K, Ca, P, S, Cl
What is the remainder of the elements of life referred to as? Trace elements, AKA micronutrients
Chemical formula Element symbols and numerical subscripts show the type and number of each atom present in the smallest unit of the substance
Types of chemical formulas Empirical formula, molecular formula, and structural formula
Empirical formula Shows the relative number of atoms of each element in the compound. Hydrogen peroxide: HO
Molecular formula Shows the actual number of atoms of each element in the molecule of the compound. Hydrogen peroxide: H2O2
Structural formula Shows the number of atoms and the bonds between them. Hydrogen peroxide: H-O-O-H
Ionic naming order Ionic compound names give the cation first and the anion second.
The relationship between the charge of common monatomic ions and their groups For cations the group number is typically the same as the charge. For anions subtract 8 by the group number to get the charge.
Compounds formed from monatomic ions: naming For cations, name is the same as the metal’s name. For anions use the root of the nonmetal name and add suffix –ide
The –ide is added to the element that gains the electron, which one is that? Nonmetal or metal? The nonmetal takes an electron from the metal, thus the nonmetal gets the –ide suffix.
Ionic compounds generally only have empirical formulas, why? Because ionic compounds are arrays of oppositely charged ions rather than a series of molecules. The only common exceptions are the mercury(I) ion and peroxides of the alkali metals.
How to name metals (especially transition metals) that can form more than one monatomic ion? By adding roman numerals to the end indicating its type. E.g. Fe^2+ is known as iron(II) and Fe^3+ is known as iron(III). For the lower-charged ions suffix: -ous, for the higher-charged ions, suffix: -ic. Thus iron(II) is AKA ferrous.
How to write polyatomic ions, e.g. calcium nitrate When two or more of the same polyatomic ion are present in the formula unit, that ion appears in parentheses, e.g. Ca(NO3)2.
Oxoanions Those polyatomic ions in which an element, usually a nonmetal, is bonded to one or more oxygen atoms.
How to name oxoanions: two oxoanions in the family With two oxoanions in the family: the ion with more O atoms: -ate. The ion with fewer O atoms: ite.
How to name oxoanions: four oxoanions in the family Ion with most O atoms: per- & -ate; ion with one fewer O atoms: -ate; ion with two fewer O atoms: -ite; least O atoms: hypo- & -ite
Hydrates Ionic compounds called hydrates have a specific number (specified by prefix) of water molecules associates with each formula unit. E.g. CaSO4*2H2O is calcium sulfate dihydtrate. Note: heating can eliminate the water molecules.
Binary acids Formed when certain gaseous compounds dissolve in water. E.g. when hydrogen chloride (HCl) dissolves in water is forms hydrochloric acid.
Oxoacids Similar to those of the oxoanions, except for two suffix changes: -ate in the anion becomes –ic in the acid. –ite in the anion becomes –ous in the acid. The oxoanions prefixes hypo- and per- are kept.
Binary covalent compounds Formed by the combination of two elements, usually nonmetals. E.g. ammonia (NH3), methane (CH4), water (H2O), etc.
Binary covalent compounds: naming The element with the lower group number is the first word in the name. Exception: when the compound contains oxygen, bromine, and iodine, the halogen is named first.
Binary covalent compounds: naming 2 If both elements are in the same group, the one with the higher period number is named first. The second element is given suffix –ide. Numerical prefixes are used at all times for second element, and only if >1 for first.
Numerical prefixes 1 – 10 Mono-, di-, tri-, tetra, penta-, hexa-, hepta-, octa-, nona-, deca-
Organic compounds: the simplest type Hydrocarbons: they contain only carbon and hydrogen
The simplest type of hydrocarbon Alkanes, such as methane, propane, butane, etc. Commonly used as fuel.
Straight-chain alkanes Alkanes with carbon chains that have no branches.
How are alkanes named? Named with a root, based on the number of C atoms in the chain, followed by the suffix –ane.
Alkanes listed from 1 – 10 Methane (CH4), Ethane (C2H6), propane, butane, pentane, hexane, heptane, octane, nonane, decane
Alkanes with branches: naming Prefix = length of the branch and the number of the carbon in the main chain that the branch is attached to. The remainder of the name is the main chain’s alkane name e.g. 2-methylbutane
Organic compounds other than alkanes; how are they named? Their names are derived from the locations of functional groups on the molecules. The functional groups, such as the hydroxyl group, determine how the compound reacts
Molecular mass AKA molecular weight, is the sum of the atomic masses in the compound. E.g. the molecular weight of H2O is 18.02.
Formula mass The mass of an ionic compound (calculated the exact same way as molecular mass)
Two broad classes of mixtures 1. Heterogeneous mixtures, 2. Homogeneous mixtures.
Heterogeneous mixtures Mixtures with one or more visible boundaries between the components. Thus, its composition is not uniform. E.g., many rocks, showing individual grains and flecks of different minerals.
Homogeneous mixtures Mixtures with no visible boundaries because the components are mixed as individual atoms, ions, and molecules. E.g. sugar fully dissolved in water is spread evenly throughout the solution.
A homogeneous mixture is also called a _____ Solution
Gaseous and aqueous solutions As the name implies, solutions can be gaseous or water-based
Laboratory separation techniques: Filtration Separates the components of a mixture on the basis of differences in particle size. It is used most often to separate a liquid (smaller particles) from a solid (larger particles)
Laboratory separation techniques: Crystallization Based on differences in solubility. The solubility of a substance is the amount that dissolves in a fixed volume of solvent at a given temperature. Method: change temperature and watch solute crystallize
Laboratory separation techniques: Distillation Separates components through differences in volatility, the tendency of a substance to become a gas. E.g. ether is more volatile than water, which is more volatile than sodium chloride.
Laboratory separation techniques: Extraction Is also based on differences in solubility. Not known: research if necessary.
Laboratory separation techniques: Chromatography A third technique based on differences in solubility. Method: send the sample through a tube containing stationary phase. Different portions of the sample will exit the tube at different rates depending on how soluble it is.
Homonuclear diatomic molecule A molecule consisting of two elements that are the same.
Standard state of an element The most stable form of an element at 1atm and 25deg Celsius. The heat of formation of an element in its standard state is zero.
Standard states of: H, N, O, F, Cl All Homonuclear diatomic molecules in gaseous state (H2(g), N2(g), etc)
Standard states: Br, Hg, P, S, I Br2(l), Hg(l), P4(s, color: white), S8(s, crystal structure: rhombic), I2(s)
Standard states: C, Si, Li, Na, K, Fe, Cu, Ag, Mg, Ca, Al, Ni, Zn, Au All solids, non-molecular
Note on ground state electron configuration: Starting from hydrogen, how far throughout the periodic table is there a pattern to the configuration as the atomic number increases? Up to Argon, then memorization is needed for everything else
Created by: Intellex_ on 2012-01-25



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