* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chapter 5
Survey
Document related concepts
Transcript
Chapter 5 Foundations of Chemistry Chemistry and Matter Chemistry is: the study of the composition of matter (the substance of the physical world) & the study of the interactions of matter with matter Beginnings of Chemistry Apothecaries – early chemists – they produced perfumes, ointments, and medicines. Characteristics of Matter • Matter occupies space two pieces cannot occupy the same space at the same time. • Matter has inertia the property of resisting changes in motion. Matter cannot be created or destroyed under normal circumstances… it can only change form. Characteristics of Matter • Matter ordinarily exists in three basic states: 1. solid – definite shape 2. liquid – assumes the shape of a container and has a definite volume 3. gas – has no definite shape or volume Characteristics of Matter One more state of matter: Plasma – when the temperature is so great that matter’s ordinary states cannot exist. Plasma typically only exists in stars…because so much heat is required. Composition of Matter The atomic theory of matter: 1. all matter consists of tiny particles called atoms. 2. all atoms of the same element have the same properties. 3. atoms can combine to make other compounds. 4. elements are composed of a single type of atom. 5. chemical processes are the result of the rearrangement, combination, or separation of atoms Atomic Theory According to atomic theory, the differences between various kinds of matter result from differences in their respective atoms or in the way their atoms are combined into molecules. Molecule: a group of atoms linked together; both elements and compound may be composed of molecules. Elements Elements are the building blocks of all substances in the universe. As of 1998 chemists had identified 115 elements, of which only 88 occur naturally in the earth; the remaining elements have been produced in the laboratory. Atomic Symbols Elements have been given designated symbols that enable scientists to recognize them and put them into chemical equations more easily… Example: Cobalt is Co Sodium is Na Kinetic Theory of Motion Particles in matter are in constant motion… The rate and energy of their motion depends upon their temperature; the higher the temperature, the faster the molecules move. Diffusion Diffusion always occurs in one direction…from higher concentration to lower … Concentrated vapors spread out into less concentrated areas… Osmosis Osmosis is the diffusion of water…it relates only to the movement of water from high to low concentration… Nuclear Chemistry Atomic Structures Atoms are composed of: Negative particles: electrons Positive Particles: protons Neutral Particles: neutrons Nuclear Chemistry Atoms Have Two Parts: 1. the nucleus 2. the orbitals The Nucleus The nucleus has two components: Protons (positive) and Neutrons (neutral) Orbitals The orbitals are the location of the fast moving charged particles: Electrons Orbitals • Orbitals are the paths the electrons follow around the nucleus. • They are also known as Energy Levels. • Energy levels are a general region of space where electrons most probably exist. Nuclear Chemistry Atomic Mass Protons and neutrons are about equal…and electrons are disregarded because they are so small… Therefore, Atomic mass is determined by adding the masses of the protons and neutrons. Nuclear Chemistry Scientists don’t use kilograms with atoms, they use a special Atomic Mass Unit Equal to 1/12 the mass of a carbon atom that has 6 protons and 6 neutrons. Thus… 1 amu is equal to the mass of 1 proton or neutron. Nuclear Chemistry To find the atomic mass of any atom simply total the number of the particles in the nucleus. Atomic Number The atomic number is the number of protons in an atom of a given element. Example: Gold It has 79 protons in the nucleus…therefore, 79 is Gold’s atomic number. Atomic Number Atoms are typically electrically neutral…they have a charge of zero! Example: Carbon has 6 protons and therefore, 6 electrons. Mass Number Mass number is the same as the atomic mass…it is the sum of the protons and neutrons. If you subtract the atomic # from the mass # you will have the # of neutrons in an atom. Mass Number Krypton has a mass # of 84 and an atomic number of 36. 84 – 36 = 48 Krypton has 48 neutrons in the nucleus. Mass Number Atoms of the same element that have different numbers of neutrons in their nuclei are called isotopes. It is indicated by a special notation called isotopic notation, which shows both the atomic number and the mass number of the element. Nuclear Radiation The emission of high-energy rays and particles (protons and neutrons) from a nucleus is called Radioactivity. Most elements are not radioactive. only elements with an atomic # over 84 are! 3 Types of Radiation Identity Charge Penetration Alpha Helium Nucleus +2 Low Beta Electron -1 Medium Gamma Electromagnetic radiation 0 High Name Symbol Types of Radiation • Beta Particles are free electrons • Gamma rays are things like x-rays and radio waves only with much more energy. Nuclear Decay When nuclear changes occur the nuclei end up with extra energy. This energy is released as Gamma Rays A meter of concrete or 2 inches of lead is required to stop Gamma Rays. Alpha Decay Alpha particles are helium nuclei. They consist of 2 protons and 2 neutrons. Beta Decay The emission of an electron from the nucleus and the transformation of the atom into a different element with the next higher atomic # is the result. Nuclear Bombardment Reactions NBRs occur when a nucleus is struck with atomic particles or other nuclei. In the 1930’s scientists discovered they could make a nucleus unstable by striking it with a nucleus. Nuclear Bombardment Reactions Stars are huge fusion reactors. Fusion reactors are safer than fission reactors, but require such extreme temperatures that we have not been successful with them. Nuclear Bombardment Reactions Nuclear fusion could be done with two hydrogen isotopes (tritium & deuterium), but would still require a temperature of 50 – 100 million kelvin. Putting the matter in a Plasma state. Nuclear Bombardment Reactions Einstein’s Theory of Relativity The Theory of Relativity shows the amount of energy released in a Nuclear Reaction: E= 2 mc Energy = mass x speed of light2 Dmetri Mendeleev Mendeleev was a Russian scientist who, in the 1860’s, began to organize the elements. He arranged them into 8 groups with similar properties. These he placed into columns. Dmetri Mendeleev Mendeleev’s “table” had gaps. Why? He predicted these to be elements that were yet to be discovered. He further predicted the properties of these “missing” elements. The Periodic Table Mendeleev organized the elements into rows by increasing atomic mass. …into columns by similar properties. His table clearly showed that the properties of the elements repeat in an orderly fashion. The Periodic Law Due to the repeating periodic pattern of the elements, Mendeleev called this… Periodic Law Classification by Atomic Number There were some problems with Mendeleev’s table arranging by atomic masses… In 1914, Henry Mosely changed the table to be arranged by atomic numbers (The number of protons in the nucleus) Periodic law is now based on atomic numbers instead of atomic masses. Periodic Law The chemical properties of the elements are periodic functions of their atomic numbers. When the elements are arranged according to their atomic numbers, the properties of the elements repeat. Electron Levels Energy Levels Neils Bohr discovered atoms had different energy levels. Electrons close to the nucleus were less energetic… Electrons further away were more energetic. Electron Levels The number of energy levels an atom has depends on the number of electrons it possesses . Electron Levels How do we know how many electrons an atom has? The number is protons (atomic number) is the same as the number of electrons. Filling Order 1. Energy levels have a limit to the # of electrons they can hold. * Two can occupy the lowest energy level. *The second can hold 8 *The third can hold 18 *The forth can hold 32 Filling Order 2. The maximum number of electrons in the outermost energy level of an atom is 8. This is called the Octet Rule. Once 8 electrons have entered an energy level, the next 2 electrons must enter a higher energy level before any unfilled lower energy level may be filled. Electron Configuration The electron configuration of an atom is the number of electrons in each energy level. Sodium Electron Configuration Filling Order Electrons in the outermost region of the atom are called Valence Electrons. Relationships Among Elements Families All the elements in a vertical column on the table have the same # of valence electrons. For example: Oxygen: 6 valence electrons Sulfur: 6 valence electrons Families Oxygen and sulfur are in the same family or group. These families have their own names… Families Group 1 (IA) Alkali metals – 1 valence electron Families Group 2 (IIA) Alkaline-earth Metals – 2 valence electrons Families Group IB – VIIIB Transition Metals – 1 or 2 valence electrons Families Group 13 (IIIA) 3 valence electrons Families Group 14 (IVA) Carbon Family – 4 valence electrons Families Group 15 (VA) 5 valence electrons Families Group 16 (VIA) Oxygen Family – 6 valence electrons Families Group 17 (VIIA) Halogens – 7 valence electrons Families Group 18 (VIIIA) Noble Gases – 8 valence electrons Inert: Non-Reactive Periods Horizontal Rows Elements in the rows have nothing in common, but it does help you know valence electrons and energy levels! Periodic Trends Metals 75% of the elements are classified as metals. Periodic Trends Metalloids • These elements have both properties of metals and nonmetals • They are semiconductors… that is… They slightly conduct electricity. Silicon is the most well known metalloid. Periodic Trends Non-Metals Hydrogen and the remaining elements on the right side of the table are non-metals.