Chapter 3 Atoms and Moles Sec. 1 Substances are made of atoms Sec. 2 Structure of atoms Sec. 3 Electron Configuration Sec 4 Counting atoms

Sec. 1 Substances are made of atoms State 3 laws that support the existence of atoms List five principles of John Dalton’s atomic theory

Atomic Theory Evidence for atomic theory did not appear until nearly 2000 years after the first idea of atoms. What do you think atoms look like?

Atomic Theory The law of definite proportions states that 2 samples of a given substance are made up of the same elements in exactly the same proportion.

Atomic Theory The law of conservation of mass states that the mass of the reactants is equal to the mass of the products

Atomic Theory The law of multiple proportions states that when elements combine, the ratio of the masses can be reduced to small whole numbers

Daltons Atomic Theory In 1808 John Dalton, an English school teacher, used the foundation set fourth by early Greeks and the three laws previously discussed to develop his own atomic theory. His theory contained 5 basic principles which can be found on page 78.

Daltons Principles All matter is composed of extremely small particles called atoms, which cannot be subdivided, created, or destroyed Atoms of a given element are identical in their physical and chemical properties. Atoms of different elements differ in their physical and chemical properties. Atoms of different elements combine in simple, whole number ratios to form compounds. In chemical reactions, atoms are combined, seperated, or rearranged but never created, destroyed, or changed

Section 2 Structure of atoms Describe the evidence for the existance of electrons, protons, and neutrons and describe the properties of these subatomic particles. Discuss atoms of different elements in terms of the numbers of electrons, protons, and neutrons, and define the terms atomic number and mass number. Define isotope, and determine the number of particles in the nucleus of an isotope.

Subatomic Particles Daltons 1st principle was the first to be found incorrect. In the mid-1800’s, scientists discovered atoms could be broken down into 3 main subatomic particles: Protons Electrons Neutrons

Subatomic Particles JJ Thompson was using a cathode ray to study electric current. He deduced that the ray must have a negative charge because it came from the negatively charged cathode. He confirmed this thought by further testing with magnetic and electric fields. He also determined the particles had mass after placing a paddle wheel in front of the beam, the beam turned the wheel.

Subatomic Particles Scientists new that atoms had no overall charge; therefore, if atoms contained negative electrons, they must also contain a positive particle as well. JJ Thompson created the plum pudding model of an atom.

Subatomic Particles Earnest Rutherford, a student of Thomson’s, disproved the plum pudding model. He performed the gold-foil experiment and discovered the positive charge of an atom was concentrated in the nucleus.

Subatomic Particles Scientists deduced that there must be a third particle because the mass of all electrons and protons in an atom did not add up to the total mass of the atom. Irene Joliot-Curie discovered a beam produced from Be atoms after they were hit with alpha particles. James Chadwick later discovered this particles had no electric charge and also belonged in the nucles.

Subatomic Particles How is the nucleus stable? Neutrons help lower the repulsive forces between the protons in the nucleus thus making it more stable.

Atomic Number Atomic number is equal to the number of protons in the nucleus. How can you determine an atoms atomic number? How can you determine the number of protons in an atom? How can you determine the number of electrons in an atom?

Mass Number The number of particles in the nucleus. Or the sum of protons and neutrons How can this number be used to determine the number of neutrons in an atom?

Atomic and Mass Number How to represent atomic and mass number of an element using a symbol

Isotopes Isotopes of an element have the same atomic number but different mass numbers due to a different number of neutrons in the nucleus. How to write isotopes, how to determine the number of particles in an isotope

Electron Configuration Combare Rutherford, Bohr, and quantum models of an atom. Explain how the wavelengths of light emitted by an atom provide information about electron energy levels. List four quantum numbers and describe their significance Write electron configurations of atoms using the Pauli exclusion principle and the aufbau princible.

Atomic Models Rutherford’s model of the atom was similar to that of planets orbiting the sun with the nucleus being the sun and electrons being the planets.

Atomic Models Bohr’s Model confined electrons to energy levels, electrons can not exist in between energy levels.

Atomic Models Electrons act as particles and waves. Particles because they have mass Waves because they move at certain frequencies(energy levels) Present day model is the electron cloud model in which orbital's are not clearly defined, but only where electrons are likely to be found.

Electrons and Light Electrons in atoms can emit light through this process. Electrons are typical at ground state, however they can become excited by absorbing energy and jump to an excited state. Once in this excited state they then fall back down to ground state and release energy

Electron Configurations Types of orbitals Energy levels How many electrons are in an energy level/orbital? How to write electron configurations

Section 4 Counting Atoms Compare the quantities and units for atomic mass with those for molar mass Define mole, and explain why this unit is used for counting atoms Calculate either mass with molar mass or number with Avogardo’s number given an amount in moles

Atomic Mass Masses of atoms are expressed in atomic mass units, the atomic mass of an element can be found where?

Intro to the Mole A mole is defined as the number of atoms in exactly 12 grams of carbon-12. A mole was a number created by scientist to make counting atoms easier. A mole is similar to a dozen.

Molar Mass Molar Mass is equal to the mass in grams of one mole of a substance. Molar mass is used to convert from grams of a substance to moles of a substance. See page 101 and 102

Avagadro’s Number Scientists determined the amount of particles (atoms, molecules, ions) to be 6.022 x 1023. See page 103