Ch 3 Atoms and Moles

Atoms Atomic theory: Democritus (400 BC) atomos. Indivisible. All substances made of atoms. Experiments support laws: Law of definite proportions: Chemical compounds always contain the same elements in exactly the same proportion by mass Law of conservation of mass: Mass can not be created or destroyed in ordinary chemical and physical changes. Law of multiple proportions: Two elements combine to form two or more compounds with a given mass of the other in ratios of small whole numbers.

Daltons atomic theory (1808) Using atomic concepts & previous pg. Laws 1. All matter is composed of extremely small particles called atoms 2. Atoms of a given element are identical in their chemical and physical properties 3. Atoms of different elements differ in their physical and chemical properties. 4. Atoms of different elements combine in simple whole number ratios to from cpds. 5. In chemical reactions, atoms are combined, separated or rearranged but never created, destroyed or changed.

Revisions #1 revised due to nuclear reaction. #2 revised due to isotopes. Diatomic molecules H2, O2 etc. Subatomic particles: proton, neutrons and electrons.

Structure of the atom Experiments to identify subatomic particles Electrons: JJ Thomson using cathode rays. Flow of particles away from negative towards positive. Plum pudding model Charge of an electron -1.602 x 10-19 C Mass of an electron 9.1 x 10-31 kg + + + +++ ---- - - + -------------- anode - cathode + <-- flow Plum pudding model

Structure of the atom Rutherford Gold leaf experiment Alpha particles directed towards gold foil Results Most past straight through, some where deflected back (1/20000) Revised model: Small dense positive charged nucleus, volume defined by locations of electrons, atom mostly empty space +

Nucleus 1/10000 the radius of the atom Protons: positive charge and 2000 time the mass of an electrons Neutral atom: # protons = # electrons Chadwick discovered neutron, no charge, mass ~ proton, located in nucleus.

Nucleus Particle symbol charge/notation mass Proton 1+1 p +1.6x10-19C/ +1 1.673x10-27kg Neutron 10n 0/0 1.675x10-27kg Protons in the nucleus repel (like charges) each other Neutrons are used to balance the repulsive force to stabilize the nucleus,

Atomic number and mass number # of protons in the nucleus, Same # for all atoms of the same element Equal the # of electrons in a neutral atom. Mass number: Sum of the number of protons and neutrons of an atom Maybe different for isotopes of the same element. Atomic structure/symbol. A = mass number, Z = atomic number X = symbol of element 1H 2H 3H 1 1 1 AX Z Protium deuterium tritium

Isotopes Atoms with same # of protons but different # neutrons. Different mass #, same atomic number. Fill in the blanks: Element symbol atomic # mass # #p #n 11 5 oxygen 16 7 8

Electron configuration Atomic models: Rutherford: positive dense nucleus and electron cloud. Bohr: positive dense nucleus, electrons in specific dist. and energies. Different energies called quantum of energy. Louis de Broglie: electrons move as waves Constructive interference and diffraction patterns. Electrons location in orbital (clouds) regions in an atom where there is a high probability of finding the electron.

Electrons and light Light: move as waves that have given frequencies, speeds and wavelength. Speed( c)= 3.0 x 108m/s, constant Wavelength (): distance between peaks, meters Frequency (): # waves per second, Hz or 1/s c= as goes updoes down Electromagnetic spectrum: range of energy,  High E& low E& short  long  Gamma x-rays ultra violet visible infrared micro TV/radio 1pm, 1020 Hz vibgyor 10km, 100kHz

Particle properties of electrons Photoelectric effect: Solar calculator Minimum frequency to move electrons Light emission: Added energy to atom, electron moves from grounded state to excited state (only certain dist.) Electron falls down to lower state and releases energy of specific  If in the visible light spectrum --> see color. Grounded state: lowest energy state of a quantized system Excited state: state at which an atom's electron; has more energy than the grounded state

Electron configuration Describes to location (probable) of each electron in an atom (grounded state) using quantum numbers. Quantum numbers/model Specific properties of electrons in an atom Electrons within an energy level are located in orbital (regions of high probability of find an electron) Four quantum numbers to describe location and properties of electrons

4 quantum numbers Principle quantum number (n): Main energy level Positive integer As n increases so does distance from the nucleus and energy of electron. Angular momentum quantum number (l): Sublevel of main energy level Indicated the shape of the sublevel (pg 96, figure 21) l = n-1 If n = 1 then l = 0, s orbital and spherical shape If n = 2 then l = 1 or l = 0, l=1 p orbital peanut shaped If n = 3 then l = 2, l =1 or l = 0, l = 2 d orbital double peanut shaped if n = 4 then l = 3, l = 2, l = 1 or l = 0, l = 3 f orbital flower shaped. 4 quantum numbers

Quantum numbers continue Magnetic quantum numbers (m): Indicate the number and orientation of orbital around the nucleus. If l = 0 the m = 0, one orbital (s) If l = 1 then m = -1, 0, +1, three orbital (p) If l = 2 then m = -2, -1, 0, +1, +2, five orbital (d) If l = 3 then m = -3, -2, -1, 0, +1, +2, +3, seven orbital (f) Spin quantum number(ms) + 1/2 Indicates the orientation of am electron’s magnetic field 2 electrons w/in an orbital have opposite spin to balance their magnetic fields

Electron configuration (short hand) Location of each electron with in an atom Rules: Pauli exclusion principle: no two electrons in the same atom will have the same 4 quantum numbers, will always have opposite spin if in the same orbital. Hund’s rule: atom in the grounded state, electrons in a sublevel will fill each orbital before pairing up Aufbau principle: electrons fill orbital from lowest energy level to highest. Use periodic table to determine order of fill Orbital notation: all 4 quantum numbers listed.

Counting atoms Atomic mass: mass of an atom expressed in atomic mass units, amu (u) Mass of p & n ~ 1 amu Atomic weight: relative average of all the isotopes of an element (g/mol) Mole (n): SI unit used to measure the amount of a substance. # of particles is the same as the number of atoms in 12.00g of carbon-12 Molar mass: mass in grams of 1 mol of a substance = to atomic weight of the element. Avogadro's number: 6.02 x 1023, number of atoms, ions, molecules or particles in 1 mole 1 mole = 6.02 x 1023 1 mole = molar mass.

Problems Calculate the mass of 5.50 mol of sodium. How many moles of helium are contained in 0.255g He? How many moles are represented by 8.0 x 1013 atoms of Ca? Calculate the mass of 4.89 x 1022 atoms of Zn. How many atoms are represented in 75.5g Ba?

Molar mass of cpds Sum of all the atomic mass within a cpd Example NaCl, BaSO4 Convert 3.91g NaCl to number of particle NaCl Convert 8.83 x 1024molecules CO2 to mass CO2