Chem 1310

Compounds can exist in different forms.

- Molecular compounds or covalent compounds • Exist as individual particles made up of bonded atoms. -Ionic compounds •Exist not as individual particles but as extended, 3D lattice structures .

Ions

- Species with a net charge. The numbers of protons and electrons in the species are not equal. Anions- Have more electrons than protons Cations - Have more protons than electrons •Ions can be either monatomic (derived from a single atom) or polyatomic (a group of atoms with an overall charge).

Rutherford's nuclear model

:•The atom's positive charge and the majority of its mass are located in a relatively small area, the nucleus. •The vast majority of the atom is empty space. Small, negatively charged electrons are spread throughout this empty space. •The number of negatively charged electrons is equal to the number of positively charged particles (protons) inside the nucleus.

Dalton's early model

Dalton's early model (a) consisted of an indivisible sphere. Thomson's plum-pudding model (b) consisted of negatively charged electrons suspended in a larger sphere of positive charge. British scientist Ernest Rutherford's gold foil experiment was designed to substantiate Thomson's plum-pudding model. Instead, it led to a new nuclear model of the atom.

Average atomic mass

For an element can be found on the periodic table along with the atomic number. -Also called atomic mass, atomic weight, or average atomic weight. Atomic mass: (fraction of isotope) x (Mass of isotope)

Example: How many neutrons are there in an atom of the isotope 60 Co?

From the periodic table, the atomic number of Co is 27.-Mass number = 60-Atomic number = protons = 27- Neutrons = mass number - atomic number-Neutrons = 60 - 27 = 33 * Note: We often think of "isotope" in terms of radioactivity. Not all isotopes are radioactive, but 60Co happens to be. Its radioactivity is exploited in GammaKnifeTM surgery to treat brain tumors.

Binary ionic compounds form

when metal atoms combine with nonmetal atoms. -Metal atoms give one or more electrons (forming cations) to nonmetal atoms (which form anions). •Compounds are electrically neutral overall Total positive charge = Total negative charge Example: Ca forms only the Ca2+ ionCl forms only the Cl- ion Two Cl- ions are required per Ca2+ to form a neutral compound: CaCl2

Atomic Masses (2.5)

-The mass of one isotope of one element was assigned a value, and the masses of all other atoms are measured relative to that standard. •Atomic mass -The weighted average of the masses of the naturally occurring mixture of isotopes of an element, compared with one-twelfth of the mass of a 12C atom

Pressure

1 atm = 760 Torr 1 atm = 760 mmHg 1 atm = 101325 Pa 1 atm = 14.7 psi 1 atm = 1.01325 bar 1 bar = 100 kPa 1 Torr = 1 mmHg

Energy

1 cal = 4.184 J 1 L·atm = 101.325 J 1 eV = 1.602×10-19 J 1 J = 1 kg·m2/s2 1 J = 1 m3·Pa 1 J = 1 L·kPa 1 J = 1 C·V

Length

1 in = 2.54 cm (exact) 1 Å = 1×10-10 m 1 mi = 5280 ft 1 mi = 1609.3 m 1 ft = 0.3048 m 1 m = 1.094 yd 1 km = 0.621 miles(mi)

Mass

1 lb = 453.6 g 1 g = 6.022×1023 amu 1 kg = 2.20 lb 1 lb = 16 oz 1 oz = 28.35 g 1 ton = 2000 lb 1 metric ton = 1 Mg

Volume

1 mL = 1 cm3 1 L = 1.0567 qt 1 gal = 3.7854 L 1 m3 = 1000 L

General Solubility Guidelines

General Solubility Guidelines Compounds of Group 1 elements (Li+, Na+, K+, Rb+, Cs+, and Fr+) or ammonium (NH4+) are soluble. Nitrates (NO3-), chlorates (ClO3-), perchlorates (ClO4-), and acetates (C2H3O2-) are soluble. Chlorides (Cl-), bromides (Br-), and iodides (I-) are soluble except for those of Ag+, Pb2+, and Hg22+. With the exception of rule 1, most carbonates (CO32-), chromates (CrO42-), phosphates (PO43-), and sulfites (SO32-) are insoluble. With the exception of rule 1 and the barium ion (Ba2+), hydroxides (OH-) and sulfides (S2-) are insoluble*. With the exception of rule 2, silver (Ag+), mercury (Hg22+), and lead (Pb2+) salts are insoluble. With the exceptions of compounds of calcium (Ca2+), strontium (Sr2+), barium (Ba2+), and the ions listed in rule 6, all sulfates are soluble. *Calcium chromate and calcium and strontium hydroxide are classified as slightly soluble, or even soluble in some textbooks. **Magnesium sulfide decomposes in water. ***Most of the oxides of Groups 1 and 2 react with water to form hydroxides.

Groups and Periods

Groups-The vertical columns of the periodic table -The modern periodic table labels the groups 1-18. Older versions use 1A-2A for the main group elements and 1B-8B for the transition metals. Roman numerals also are used frequently in older versions. •Periods-The horizontal rows of the periodic table

Example:

How many protons and electrons are there in the chlorine atom? In the chlorine ion (Cl-)?-Chlorine atom = Cl-From the periodic table, Cl has 17 protons. In the neutral atom, there are also 17 electrons.-Chloride ion = Cl--The chlorine atom gained one electron to form an anion. The chloride ion thus has 17 protons and 18 electrons.

Seven elements occur as diatomic molecules when they are in their elemental form.

Hydrogen Nitrogen Oxygen Fluorine Chloride Bromine Iodine

Atoms are electrically neutral:

Number of protons = number of electrons •Atomic numberis the number of protons in the nucleus of an atom. -All atoms of a given element have the same number of protons (the atomic number identifies the element). 14Subatomic Particles, Isotopes, and Ions (2.4)

Subatomic Particles, Isotopes, and Ions (2.4)

Protons, neutrons, and electrons are subatomic particles .•The nucleus comprises almost all of the mass of an atom whereas most of the volume is occupied by electrons.

Significant Figures

Scientists imply the level of precision in measurements by how they report the number. Unlike in mathematics where 25 and 25.0 are identical, a measurement of 25 cm in science means something drastically different than a measurement of 25.0 cm.Scientific measurements are reported to one digit more than what is known with certainty. A reported value of 25 cm implies that the actual value is somewhere between 24 cm and 26 cm, approximately. In contrast, a reported value of 25.0 cm implies that the actual value is somewhere between 24.9 cm and 25.1 cm, approximately. Counting Significant FiguresTo know which digits in a number are "significant", first let's go over some terminology. Non-zero digits are 1, 2, 3, 4, 5, 6, 7, 8, and 9 (any digit other than zero). Leading zeros are those that come before all the non-zero digits (but not necessarily before the decimal point). Trailing zeros are those that come after all the non-zero digits (but not necessarily after the decimal point).Rule 1: Non-zero digits are always significant. For example, 25 has two significant figures.Rule 2: Leading zeros are never significant. For example 0.025 has two significant figures.Rule 3: Trailing zeros are significant if a decimal point is shown in the number, but may or may not be significant if no decimal point is shown. By convention, it is assumed that trailing zeros without a decimal point are not significant. For example, 250.0 has four significant figures, but 2500 only has two definitive significant figures. In these cases, it is best to write the number in scientific notation to avoid ambiguity.Rule 4: Zeroes that are between non-zero digits are always significant. RoundingYou will often need to round calculated numbers to the proper number of significant figures. For example, 25.18 rounded to one significant figure is 30, rounded to two significant figures is 25, and rounded to three significant figures is 25.2.How would you round a number like 99.99 to three significant figures? You could either write 100. or 1.00×102. Multiplication and Division of MeasurementsThe number of significant figures in the product or quotient of two or more measurements cannot be greater than that of the measurement with the fewest significant figures. For example: 25.0 × 1.0 = 25 Addition and Subtraction of MeasurementsThe number of digits after the decimal point in the sum or difference of two or more measurements cannot be greater than that of the measurement with the fewest digits after its decimal point. For example: 25.0 + 1 = 26 Logarithms and Antilogs The number of digits after the decimal point of log(x) should be equal to the number of significant figures of x. For example: log (3.5×105) = 5.54 For an inverse log of x (10x), the number of significant figures in the answer should be equal to the number of digits after the decimal point in x. For example: 10-3.421 = 3.79×10-4 Multi-step CalculationsWhen doing a series of mathematical operations, you should not round at each individual step. You should keep track of the number of significant figures produced at each step, then round at the end.For example: (30.62 ÷ 2.0) + 0.4 = 16To arrive at this answer, you would first analyze each step...1) 30.62 ÷ 2.0 = 15.31. If rounded, the result would have only have two significant figures, and thus no digits after the decimal point.2) Take the unrounded value, 15.31, and add 0.4. 15.31 + 0.4 = 15.71. From step 1, we know the result should have no digits after the decimal point, and so we round to the ones place, 15.71 ≈ 16.You may be wondering, "Why is 16 a better answer than 15.71? Isn't the number more accurate with more digits?". But remember, the original values (30.62, 2.0, and 0.4) each have some degree of error in them (since nearly everything in science is a measurement). If we report the answer as 15.71, we imply that we know it's between 15.70 and 15.72, and that is simply not true. The accumulated error puts the ones place in doubt, so by reporting the answer as 16 we imply that it's roughly between 15 and 17.

Temperature

TK = TC + 273.15 TC = (5/9)(TF - 32) TF = 32 + (9/5)TC

The periodic table is an organization of elements by

The periodic table is an organization of elements by increasing atomic number with elements having similar chemical properties aligned in vertical columns.

Isotopes

are atoms of the same element that have different numbers of neutrons. •C-14 has a mass number of 14 while C-12 has a mass number of 12. •C-14 has 14 - 6 = 8 neutrons while C-12 has 12 - 6 = 6 neutrons.

Polyatomic ions

are groups of two or more bonded atoms that have lost or gained electrons, and thus have an overall net charge .

Chemical formulas

combine elemental symbols and subscripts to represent chemical compounds. -Provide information about the relative number of atoms of each element -Sometimes also give information about the arrangement of atoms in the molecule. The group of atoms represented by a chemical formula is called a formula unit. -An atom or molecule of an uncombined element, a molecule of a covalent compound, or a set of ions in an ionic compound

English physicist J.J. Thomson

discovered the negatively charged subatomic particle now known as the electron in the late 1800s.•American physicist Robert Millikan succeeded in measuring the mass of a single electron in the early 1900s.-Because atoms are neutral overall, the "non-electron" part of the atom must have a positive charge equal to the negative charge of electrons.-The electron accounted for only 1/1836 of the mass of a hydrogen atom.-These observations led to Thomson's plum-pudding model of the atom.

JohnDalton

formulated his atomic theory to explain the laws of chemical combination: 1.Matter is made up of very tiny, indivisible particles called atoms. 2.Each atom of a particular element has the same mass, but the mass of an atom of one element is different from the mass of an atom of any other element. 3.Atoms combine to form what we now call molecules. When they do so, they combine in small, whole-number ratios. 4.Atoms of some pairs of elements can combine with each other in different, small, whole-number ratios to form different compounds.

The law of conservation of mass

is just one of three laws of chemical combination observed, but not understood, by early chemists: - The law of definite proportions states that any given compound is composed of definite proportions, by mass, of its elements. -The law of multiple proportions refers to compounds that are composed of the same elements (CO and CO 2, for example). It states that, for a given mass of one of the elements, the ratio of the masses of any other element in the compounds is a small, whole-number ratio.

Mass number

is the number of protons plus the number of neutrons in an atom.