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The Atom Nucleus Electron Shell or Orbit
The Atom.
What are the 3 major parts of an atom? Proton Neutron Electron
Stoichiometry Atomic Mass The Mole concept Molar Mass Percent Composition of Compounds Determination of Formula of Compounds Writing and Balancing Chemical Equations Interpreting balance equations, and Reaction Stoichiometry and Calculations
Atomic Masses Absolute masses of atoms cannot be obtained too small to measure the mass directly; Relative atomic masses are used instead masses relative to a chosen standard or reference. Carbon-12 is used as atomic mass reference it is assigned an atomic mass of 12 u exactly; Other atoms are assigned masses relative to that of carbon-12; Relative atomic masses are determined using mass spectrometer;
Carbon-12 Chemists have defined the carbon-12 atom as having a mass of 12 atomic mass units.
The Mole: Molar Quantity A quantity that contains the Avogadro s number of items; Avogadro s number = 6.02 x 10 23 1 mole = 6.02 x 10 23 (atoms, molecules, ions) 12.01 g of carbon contains the Avogadro s number of carbon atoms. 1 mole of carbon = 12.01 g = 6.02 x 10 23 atoms
Gram-Atomic Mass Mass of 1 carbon 12 C =12 atom = 12 u Mass of 1 mole of carbon-12 = 12 g; Mass of 1 oxygen atom = 16.00 u Mass of 1 mole of oxygen = 16.00 g Gram-atomic mass = mass (in grams) of 1 mole of an element that is, the mass (in grams) that contains the Avogadro s number of atoms of that element. gram-atomic mass is the molar mass of an element in grams.
Atomic Mass & Gram-Atomic Mass Examples: Element Atomic mass Gram-atomic mass Carbon 12.01 u 12.01 g/mol Oxygen 16.00 u 16.00 g/mol Aluminum 26.98 u 26.98 g/mol Silicon 28.09 u 28.09 g/mol Gold 197.0 u 197.0 g/mol
Molecular Weight = Molecular Mass = Molar Mass Molecular weight = the sum of atomic masses Molecular mass = the mass of a molecule in u; Molar mass = the mass of one mole of an element or a compound, expressed in grams. Examples: Molecular Mass Molar Mass N 2 28.02 u 28.02 g/mol H 2 O 18.02 u 18.02 g/mol C 8 H 18 114.22 u 114.22 g/mol
Calculating Molecular weight Calculating the molecular weight of sucrose, C 12 H 22 O 11 : (12 x 12.01 g) + (22 x 1.008 g) + (11 x 16.00 g) = 342.3 g/mole Molecular weight of ammonium hydrogen phosphate, (NH 4 ) 2 HPO 4 : (2 x 14.01 g) + (9 x 1.008 g) + (1 x 30.97 g) + (4 x 16.00 g) = 132.06 g/mole
Polyatomic elements 1 mole molecular weight(g) 6.02 x 10 23 molecules
General Review 1 mole 6.02 x 10 23 (atoms, molecules, ions) Monoatomic 1 mole 6.02 x 10 23 atoms Polyatomic 1 mole 6.02 x 10 23 molecules
How you measure how much? You can measure mass, or volume, or you can count pieces. We measure mass in grams. We measure volume in liters. We count pieces in MOLES.
The abbreviation SI comes from the French le Système International. *These prefixes are commonly used in chemistry. This is the Greek letter _(pronounced mew ).
Energy is defined as the capacity to do work or to transfer heat. Energy can be classified into two principal types: 1- kinetic energy The energy of motion. 2- Potential energy: - Energy due to condition, position, or composition. - Associated with forces of attraction or repulsion between objects. Nuclear energy is an important kind of potential energy. The Law of Conservation of Energy: Energy cannot be created or destroyed in a chemical reaction or in a physical change. It can only be converted from one form to another.
Atoms, Molecules and Ions Chapter 2
Dalton s Atomic Theory (1808) 1. Elements are composed of extremely small particles called atoms. 2. All atoms of a given element are identical, having the same size, mass and chemical properties. The atoms of one element are different from the atoms of all other elements. 3. Compounds are composed of atoms of more than one element. In any compound, the ratio of the numbers of atoms of any two of the elements present is either an integer or a simple fraction. 4. A chemical reaction involves only the separation, combination, or rearrangement of atoms; it does not result in their creation or destruction.
The smallest particle of an element that maintains its chemical identity through all chemical and physical changes is called an atom (Figure 2-1). Figure 2-1 Relative sizes of monatomic molecules (single atoms) of the noble gases.
A molecule is an aggregate(combine) of two or more atoms in a definite arrangement held together by covalent bonds. H 2 H 2 O NH 3 CH 4 A diatomic molecule contains only two atoms
A polyatomic molecule contains more than two atoms
Dalton s Atomic Theory 2
16 X + 8 Y 8 X 2 Y
Atom, Atomic number, and Mass number An atom contains equal numbers of electrons and protons. Atomic number (Z) = number of protons in the nucleus. Mass number (A) = number of protons + number of neutrons. Mass Number Atomic Number A Z X Element Symbol Atomic Number Element Symbol 2.3
Atomic mass is the mass of an atom in atomic mass units (amu) Atomic mass unit (amu), which is defined as exactly 1/12 of the mass of an atom of a particular kind of carbon atom, called carbon-12. By definition: 1 atom 12 C weighs 12 amu On this scale 1 H = 1.00794 amu 16 O = 15.9994 amu
Moles Defined as the number of carbon atoms in exactly 12 grams of carbon-12. 1 mole contains 6.02 x 10 23 particles. 6.02 x 10 23 is called Avogadro s number.
Representative particles The smallest pieces of a substance. For a molecular compound it is a molecule. For an ionic compound it is a formula unit. For an element it is an atom.
The gram atomic weight of an element is the mass in grams of one mole of an elemen that is numerically equal to its atomic weight. The gram molecular weight is the gram formula weight of a molecular compound. The gram formula weight of a compound is the mass in grams of one mole of the ionic compound that is numerically equal to its formula weight. The gram formula weight of a compound is the sum total of all the individual atomic weight in the formula.
The mole (mol): Mole Calculations Amount of a substance that contains as many elementary entities (atoms, molecules or other particales) as the number of atoms in isotopically pure 12 C 1 mol = N A = 6.0221367 x 10 23 1 mol 12 C atoms = 6.02 x 1023 12C atoms Avogadro s number (N A ) 1 mol H 2 O molecules = 6.02 x 1023 molecules 1 mole NO -3 ions = 6.02 x 1023 NO3- ions.
Molar mass is the mass of 1 mole of eggs shoes marbles atoms in grams Defined as the number of grams of 1 mole of atoms,ions,or molecules. 1 mole 12 C atoms = 6.022 x 10 23 atoms = 12.00 g 1 12 C atom = 12.00 amu 1 mole 12 C atoms = 12.00 g 12 C 1 mole lithium atoms = 6.941 g of Li For any element atomic mass (amu) = molar mass (grams)
Molar Mass The atomic mass of any substance expressed in grams corresponds to 1 mol of the substance. Atomic mass of a substance expressed in grams is the molar mass. The molar mass of a diatomic substance is equal to twice its atomic mass.
Do You Understand Molar Mass? Calculate the number of sodium atoms in 0.120 mol Na? 1 mol of Na = 6.022 x 10 23 atoms of Na 1 mol of Na 6.022 x 10 23 atoms of Na 0.120 mol Na X? atoms of Na 0.120 mol Na x 6.02 x 1023 atoms Na = 7.22 x 1022 1 mol Na
Do You Understand Molar Mass? How many atoms are in 0.551 g of potassium (K)? 1 mol of K = 39.10 g of K 1 mol of K = 6.022 x 10 23 atoms of K 6.022 x 10 23 atoms of K 39.10 g of K X? atoms 0.551 g of K 0.551 g K 39.10 g K x 6.022 x 10 23 atoms of K = 8.49 x 10 21 atoms of K
One Mole of: C S Hg Cu Fe 3.2
EXAMPLE 1 Moles of Atoms How many moles of atoms does 136.9 g of iron metal contain? Solution 1 mol Fe atoms 55.85 g Fe?_ mol Fe atoms 136.9 g Fe EXAMPLE 2 Moles of Atoms How many grams of copper "Cu" are there in 2.55 mole of Cu [atomic mass of Cu = 63.5] Solution 1 mol Cu atoms 63.5 g Cu? 2.55 mol Fe atoms?_ g Cu
EXAMPLE. 32.0 g C, 6.7g H, 18.7g N, 42.6g O. Convert grams into moles: 1 mol C 12.01 g C X? mole 32.0 g C 32.0 g C x 1 mol = 2.66 mol C 12.01 g C 6.7 g H x 1 mol H = 6.6 mol H 1.01 g H
Molecular mass (or molecular weight) is the sum of the atomic masses (in amu) in a molecule. SO 2 1S 2O SO 2 32.07 amu + 2 x 16.00 amu 64.07 amu For any molecule molecular mass in amu = molar mass in grams 1 molecule of SO 2 weighs 64.07 amu 1 mole of SO 2 weighs 64.07 g
How to calculate molecular mass for a compound Ex. H 2 O Atomic masses H = 1, O = 16 Molecular mass of H2O = [ 1x2] +16 = 18 One mole of H 2 O = 18 gram H 2 O Ex. CO 2 Atomic masses C = 12,O = 16 Molecular mass of CO 2 = 12 +[16 x 2] = 44 One mole of CO 2 = 44 gram CO 2
Ex. NaOH Atomic masses Na = 23, H = 1,O = 16 Molecular mass of NaOH = 23+ 16+1 = 40 One mole of NaOH = 40 gram NaOH Ex. molecular weight Calculate the molecular weight of acetic acid, CH 3 COOH? Atomic masses C = 12, H = 1,O = 16 Molecular mass of CH 3 COOH = [12x2[ + ]16x2] + [1x4] = 60 One mole of CH 3 COOH = 60 gram CH 3 COOH
Formula mass is the sum of the atomic masses (in amu) in a formula unit of an ionic compound. NaCl 1Na 1Cl NaCl 22.99 amu + 35.45 amu 58.44 amu For any ionic compound formula mass (amu) = molar mass (grams) 1 formula unit of NaCl = 58.44 amu 1 mole of NaCl = 58.44 g of NaCl
Do You Understand Formula Mass? What is the formula mass of Ca 3 (PO 4 ) 2? 1 formula unit of Ca 3 (PO 4 ) 2 3 Ca 3 x 40.08 g/mol 2 P 2 x 30.97 g/mol 8 O + 8 x 16.00 g/mol 310.18 g/mol Units of grams per mole are the most practical for chemical calculations!
Percent composition of an element in a compound = n x molar mass of element molar mass of compound x 100% n is the number of moles of the element in 1 mole of the compound (assume you have 1 mole!). C 2 H 6 O 2 x (12.01 g) %C = 46.07 g 6 x (1.008 g) %H = 46.07 g 1 x (16.00 g) %O = 46.07 g x 100% = 52.14% x 100% = 13.13% x 100% = 34.73% 52.14% + 13.13% + 34.73% = 100.0%
An empirical formula represents the simplest whole number ratio of the atoms in a compound. The molecular formula is the true or actual ratio of the atoms in a compound.
An empirical formula shows the simplest whole-number ratio of the atoms in a substance. Calculated the empirical formula 1- Turn % by mass into gram by assuming a 100 g of sample 2- Turn grams of each element into mole of the element by dividing by atomic mass. 3- divide the mole of each elemental by the smallest number of moles. 4- determine the empirical formula by multiplying each result by the appropriate integer.
EXAMPLES molecular H 2 O C 6 H 12 O 6 O 3 empirical H 2 O CH 2 O O N 2 H 4 NH 2 A. What is the empirical formula for C 4 H 8? 1) C 2 H 4 2) CH 2 3) CH B. What is the empirical formula for C 8 H 14? 1) C 4 H 7 2) C 6 H 12 3) C 8 H 14 C- What is a molecular formula for CH 2 O? 1) CH 2 O 2) C 2 H 4 O 2 3) C 3 H 6 O 3
EXAMPLE If the molecular formula has 4 atoms of N, what is the molecular formula if SN is the empirical formula? Explain. Solution 1) SN 2) SN 4 3) S 4 N 4 3) S 4 N 4 If the actual formula has 4 atoms of N, and S is related 1:1, then there must also be 4 atoms of S. EXAMPLE A compound has a formula mass of 176.0 and an empirical formula of C 3 H 4 O 3. What is the molecular formula? 1) C 3 H 4 O 3 2) C 6 H 8 O 6 3) C 9 H 12 O 9
Solution 2) C 6 H 8 O 6 Atomic masses C = 12, H = 1, O = 16 Formula mass (Molecular mass) of C 3 H 4 O 3 = [12x3[ + ]1x4] + [16x3] = 88 C 3 H 4 O 3 = 88.0 g/ef EXAMPLE 176.0 g 88.0 = 2.0 If there are 192.0 g of O in the molecular formula, what is the true formula if the EF is C 7 H 6 O 4? 1) C 7 H 6 O 4 2) C 14 H 12 O 8 3) C 21 H 18 O 12
Finding the Molecular Formula EXAMPLE A compound is Cl 71.65%, C 24.27%, and H 4.07%. What are the empirical and molecular formulas? The molar mass is known to be 99.0 g/mol. Solution 1- State mass percents as grams in a 100.00-g sample of the compound. Cl 71.65 g C 24.27 g H 4.07 g 2- Calculate the number of moles of each element. 71.65 g Cl x 24.27 g C x 4.07 g H x 1 mol Cl 35.5 g Cl 1 mol C 12.0 g C 1 mol H 1.01 g H = = = 2.02 mol Cl 2.02 mol C 4.04 mol H
Why do you need the number of moles of each element in the compound? 3. Find the smallest whole number ratio by dividing each mole value by the smallest mole values: Cl: 2.02 = 1 Cl 2.02 C: 2.02 = 1 C 2.02 H: 4.04 = 2 H 2.02 4- Write the simplest or empirical formula CH 2 Cl 5- EM (empirical mass) = 1 ( C ) + 2 ( H ) + 1 (Cl) = 49.5 6- n = molar mass/empirical mass Molar mass = 99.0 g/mol = n = 2 E M 49.5 g/em 7-Molecular formula (CH 2 Cl) 2 = C 2 H 4 C l2
A compound of carbon and oxygen is found to contain 27.3% carbon and 72.7% oxygen by mass. Carbon Oxygen Calculate the amount in moles 27.3 = 2.27 Divide the number of moles by smallest Obtain the simplest whole number mole ratio 12.0 2.27 = 1 2.27 1 2 72.7 = 4.54 16.0 4.54 = 2 2.27
9.0g of a compound of only C,H,O contains 4.8 g of O and 3.6g of C C H O m(g) 3.6 9 (4.8+3.6) = 0.6 n(mol) 3.6 =0.3 Divide by smallest mol 12.0 0.3 = 1 0.3 0.6 = 0.6 1.0 0.6 = 2 0.3 Ratio 1 2 1 4.8 4.8 = 0.3 16.0 0.3 = 1 0.3
Percent Composition and Empirical Formulas Determine the empirical formula of a compound that has the following percent composition by mass: K 24.75%, Mn 34.77%, O 40.51% percent. n K = 24.75 g K x n Mn = 34.77 g Mn x 1 mol K 39.10 g K = 0.6330 mol K 1 mol Mn = 0.6329 mol Mn 54.94 g Mn n O = 40.51 g O x 1 mol O 16.00 g O = 2.532 mol O To begin, assume for simplicity that you have 100 g of compound!
Percent Composition and Empirical Formulas n K = 0.6330, n Mn = 0.6329, n O = 2.532 0.6330 K : ~ 1.0 0.6329 Mn : 0.6329 0.6329 = 1.0 2.532 O : ~ 4.0 0.6329 KMnO 4