2 Greek philosophers devised a theory of atoms, or tiny particles. John Dalton combined the idea of elements with the Greek theory of the atom.Matter is made up of atomsAtoms cannot be divided into smaller piecesAll atoms of an element are made of different atomsDifferent elements are made of different atomsDalton’s theory was tested by William Crookes and his cathode ray tube experiment
3 C. J.J. Thomson discovered negatively charged particles, electrons, which are part of every atom. 1. Thomson revised Dalton’s model to include a sphere with a positive charge and negatively charged electrons spread evenly within the positive charge 2. The negatively charged electrons and the positively charge in the sphere neutralize each other
4 D. Earnest Rutherford tested Thomson’s model, which was found to be an inaccurate model of the atom. E. An atomic model with a nucleus was developed. 1. The positively charged proton is located in a very small space at the center of an atom 2. Most of an atom is empty space occupied by nearly mass less electrons. 3. Electrically neutral particles, neutrons, are also located in the nucleus. 4. The number of electrons equals the number of protons in an atom
5 F. The electron cloud model explains the unpredictable wave behavior of electrons, which could be anywhere in the area surrounding the nucleus.
6 A. Atomic Number- number of protons in the nucleus of an atom Section 2 The NucleusA. Atomic Number- number of protons in the nucleus of an atom1. isotopes of an atom have the same number of protons but different number of neutrons. 2. Mass number is the number of neutrons plus the number of protons3. Average atomic mass- the average mass of the mixture of an element’s isotopes.4. The strong nuclear force holds tightly packed protons together in a nucleus
7 B. Radioactive Decay occurs when an atom releases nuclear particles and energy. 1. When a proton is released, one element changes into another, a process called transmutation.
8 2. Alpha Particlea. 2 protons and 2 neutrons, are released during transmutationb. Atomic number decreases
9 3. Beta Particlea. A high energy electron from the nucleus is released with energy when an unstable neutron splits into an electron and a proton.b. Atomic number increases by one
10 C. Half-life of a radioactive isotope is the amount of time it takes for half of the sample to decay 1. Half lives range in length from fractions of a second to billions of years. 2. Carbon-14 dating is used to determine the age of artifacts and fossils.
11 3. Radioactive waste must be disposed of carefully to avoid harming people and the environment
12 D. Synthetic elements are made in labs by smashing atomic particles into a target element. 1. Radioactive Isotopes from artificial transmutation are called tracer elements and can be used for medical purposes. 2. Tracer elements are also used to study the environmental impact of pesticides and fertilizers and to locate water resources.
13 Section 1 Introducing the Periodic Table Chapter 15Section 1 Introducing the Periodic TableBy 1830 fifty-five different elements had been isolated and named.In 1869 Mendeleev arranged elements in order of increasing atomic mass and found that elements with similar properties fell into groups.Moseley improved the periodic table by arranging the elements according to atomic number instead of atomic mass
14 B. The modern periodic table contains seven periods or rows of elements whose properties change gradually and eighteen groups of columns, each with a family of elements having similar properties 1. Groups 1 and 2 along with groups 13 thru 18 are called the representative elements. 2. Groups 3 and 12 are called the transition elements.
15 3. A metal has luster, conducts heat and electricity, is malleable and ductile. 4. Nonmetals are usually gases or brittle solids at room temperature 5. A metalloid shares properties with metals and nonmetals 6. Symbols are abbreviation often base on the elements name.
16 Section 2 Representative Elements Groups 1 and 2 are active metals found in nature combined with other elements; although hydrogen is placed in Group 1, it is not a metal and it shares properties with Groups 1 and 17Alkali metals- silvery solids with low densities and low melting points; they increase in reactivity from top to bottom of the periodic tableAlkaline earth metals- are denser, harder, have higher melting points, and are slightly less reactive than alkali metals in the same period.
17 B. Groups 13 through 18 may contain metals, nonmetal, or metalloids in solid, liquid, or gas form. 1. The Boron family elements in group 13 are all metals except boron, which is a metalloid; these elements are used in a variety products.
18 The carbon group elements are all metalloids or metals, except for carbon itself. a. carbon is found in all living things and exists in several forms.b. Silicon and germanium are used in electronics as semiconductorc. Tin and lead are the two heaviest elements in Group 14
19 3. The nitrogen group contains nitrogen and phosphorous, which are required by living things and which are used in industry 4. The oxygen family contains oxygen and sulfur, which are essential for life and used to manufacture many products. 5. The halogen groups elements form salts with sodium and with other alkali metals 6. The noble gases rarely combine with other elements; they are often used in lighting and inflating balloons
20 Section 3 Transition elements Groups 3 to 12 are the transition elements; most are combined with other elements in ores.The iron triad is composed of iron, cobalt, and nickel; these metals have magnetic properties.Several transition elements can be used as catalysts, which are substances that make reactions occur faster without changing itself
21 B. The inner transition elements are called lanthanides and actinides B. The inner transition elements are called lanthanides and actinides. 1. The lanthanides are soft metals and were once thought to be rare. 2. All the actinides are radioactive; several are synthetic elements that do not occur naturally. 3. Dental materials are sometimes made of new composites, resins, and porcelains.
23 Section 1 Why do atoms combine? Chapter 16Section 1 Why do atoms combine?The nucleus, containing protons and neutrons, is at the center of an atom and is surrounded by the electron cloud, an area of space around the nucleus where electrons travel.1. Electrons have a negative charge and do not travel in well-defined orbits.2. Each element has a different atomic structure consisting of a particular number of protons, neutrons and electrons
24 B. The number and arrangement of electrons in the electron cloud determines the physical and chemical properties of the element. 1. Electrons are arranged in different energy levels at different distances from the nucleus 2. The farther an energy level is from the nucleus, the more electrons it can hold. 3. Electrons in the level closest to the nucleus have the lowest amount of energy; electrons farthest from the nucleus have highest amount of energy
25 C. Data from the periodic table can be used to understand energy levels. 1. The atomic number is the same as the number of protons in an electrically neutral atom2. The number of electrons in an element’s outermost energy level increases from left to right across a period.a. The first energy level is complete with two electrons, and the first period has two elements.b. The last element in each of the other periods has eight electrons in its outer energy level.
27 3. Each column in the periodic table contains one element family or group with similar chemical properties. a. The noble gases in Group 18 do not combine easily with other elements because their energy levels are stable. b. The halogens have 7 electrons in their outer energy levels; reactivity of the halogens decreases down the group. c. The alkali metals in Group 1 have one electron in their outer energy level; reactivity of the alkali metals increases down the group
28 D. An electron dot diagram is the symbol for the element surrounded by as many dots as there are electrons in its outer energy level. 1. Dots are written on four sides of the element symbol. a. One dot represents a single electron b. Paired electrons are represented by two dots.
31 2. A chemical bond is the force that holds two atoms together a 2. A chemical bond is the force that holds two atoms together a. Electron dot diagrams can be used to show how atoms bond with eachother b. Atoms bond with other atoms so that each atom has a stable energy level
32 Section 2 How Elements Bond A. Atoms form bonds by losing electrons, by gaining electrons, by pooling electrons, or by sharing electrons.1. An atom that is no longer neutral because it has lost or gained an electron is called an ion.2. An ionic bond forms when positive and negative ions attract each other.a. Sodium Chloride is formed from sodium ions and chloride ions.b. Two or more elements that are chemically bonded form a compound.
33 B. Metallic bonds form when metal atoms share their pooled electrons. 3. Some atoms can gain or lose more than one electron when they form ions.B. Metallic bonds form when metal atoms share their pooled electrons.
34 C. A covalent bond forms between atoms that share electrons. 1. Atoms sharing electrons form a neutral particle called a moleculea. Covalently bonded compounds are called molecular compounds.b. No electrons are involved in a double bond.