Unit 3 Test Study Guide Name: (Highlight the information that answers the questions on the right then write the answer in the box.

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1 Unit 3 Test Study Guide Name: (Highlight the information that answers the questions on the right then write the answer in the box.) Identify that protons determine an element's identity and valence electrons determine its chemical properties, including reactivity. Each element has a unique number of protons in all of its atoms. The atomic number of an element is the number of protons in each of its atoms. To identify which element a model of an atom is depicting, count the number of protons in the nucleus and find the element on the periodic table with that atomic number. The total number of electrons in an (electrically neutral) atom equals the number of protons. In the Bohr Model of the atom, electrons fill different electron orbitals (also known as electron shells or energy levels) from the insideout. The first orbital can only hold 2 electrons. The second orbital can hold 8 electrons, the third can hold up to 18, but the outermost orbital can never have more than 8 electrons. Only these outermost electrons, known as valence electrons, can interact with other atoms in chemical reactions. In general, elements with the same number of valence electrons, usually found in the same group on the periodic table, have similar chemical properties. Atoms are most stable, and thus will not react with other atoms, when their outer (valence) electron orbital is completely full. For the period 1 elements, this is two electrons; for other elements, this is eight electrons. All of the group 18 elements, known as the noble gases, have a full valence electron orbital, and thus are completely nonreactive. Atoms that only have one valence electron (group 1 elements) are very reactive, because they need only lose that one electron in a reaction to expose an inner full electron orbital and become stable (hydrogen excepted). Atoms that have 7 valence electrons (group 17 elements) are very reactive, because they need only gain one electron in a reaction to complete their outer valence electron orbital. 1. What is the atomic number? 2. How can you identify an atom when looking at a model? 3. How do we determine the number of electrons in an electrically neutral atom? 4. How many electrons can the 1 st energy level hold? 2 nd? 3 rd? 5. What are valence electrons? 6. What determines an atom s stability/reactivity? 7. Which two electron configurations for atoms are the most reactive? 8. What is an element? Interpret the arrangement of the Periodic Table, including groups and periods, to explain how properties are used to classify elements. An element is a substance that cannot be separated into simpler substances by physical or chemical means. An element is already in its simplest form. 9. What is an atom?

2 The smallest piece of an element that still has the properties of that element is called an atom. An element is a pure substance, containing only one kind of atom. The Periodic Table of Elements is a list of all the elements that have been discovered and named, with each element listed in its own element square. Elements are represented on the Periodic Table by one or two letter symbol, and its name, atomic number and atomic mass. The elements are listed on the Periodic Table in atomic number order, starting at the upper left corner and then moving from the left to right and top to bottom, just as the words of a paragraph are read. The element s atomic number is based on the number of protons in each atom of that element. In electrically neutral atoms, the atomic number also represents the number of electrons in each atom of that element. The element s atomic mass as shown on the periodic table, is the average sum of protons and neutrons in each atom of that element. To calculate the number of neutrons in an element, subtract the atomic number from the rounded atomic mass. For example, the atomic mass of iron is 55.84, which rounds up to 56. Iron s atomic number is 26. The number of neutrons is thus = 30. The horizontal (left-to-right) rows of the periodic table are called periods. There are seven periods in the periodic table. Within each period, all elements have the same number of occupied Bohr Model electron shells (electron energy levels or orbitals). There are 7 periods. The vertical (up-and-down) columns indicate the 18 different groups or chemical families of the periodic table, usually numbered 1 through 18, from left to right. The elements within each group have the same general chemical properties, reactivity, and the same number of valence electrons in the Bohr Model outer electron shell. Compare metals, nonmetals, and metalloids using physical properties such as luster, conductivity, or malleability Most versions of the periodic table include color coding for the three metal classifications for the elements: metals, metalloids, and nonmetals. Other periodic tables, like the one used on the STAAR test, use a zigzag dividing line to show the location of the metalloids. 10. What information can be found in a Periodic Table square? 11. How are the elements arranged? 12. What makes up an atom s atomic mass? 13. How do you calculate the number of neutrons in an element? 14. What are periods? 15. What do atoms in the same period have in common? 16. What are groups? 17. What do atoms in the same group have in common? 18. Where are metals located on the periodic table?

3 Metals occupy most of the periodic table. Metals generally have a metallic luster, and conduct heat and electricity well. They are usually malleable, meaning they can be beat into shapes (like an iron horseshoe), and ductile, meaning it can be drawn into a shape (like copper wire). All metals except mercury are solids at room temperature. Metalloids occupy a diagonal strip of elements between the metals on the left side of the periodic table and the non-metals on the right side, including boron, silicon, arsenic, tellurium and astatine to the right of the dividing line, and antimony, germanium and polonium to the left of the line. They are coded green in the textbook s periodic table. All metalloids are solid at room temperature. Metalloids generally have properties between the metals and non-metals. They can conduct electricity, but not as well as metals, and only under certain circumstances. Unlike metals, most metalloids are brittle, not ductile. Semi-conductors used in electronic devices are made from the metalloids silicon and germanium. Non-metals include gases like hydrogen, oxygen, nitrogen, fluorine, chlorine and the noble gases, and solids like carbon, phosphorus, sulfur, and iodine, as well as one liquid (bromine). They are coded yellow in the textbook s periodic table, and are located to the right of the metalloid dividing line (except hydrogen, at the upper left corner of the periodic table). Non-metals do not conduct heat or electricity well. When solid, they are usually brittle. The non-metal elements hydrogen, carbon, oxygen, nitrogen, sulfur and phosphorus are essential to life. Describe the structure of atoms, including the masses, electrical charges, and locations, of protons and neutrons in the nucleus and electrons in the electron cloud. Atoms are the smallest particle of an element. Each element is made of only one kind of atom. For example, gold is only made of gold atoms and neon is only made of neon atoms. The overall shape of all atoms is spherical (like a basketball), but they vary in size. Each atom has a nucleus located at its center, surrounded by an electron cloud, which is mostly empty space outside of the nucleus. The nucleus is very small, compared with the overall size of the atom. Atoms are made of three different kinds of sub-atomic particles: protons, neutrons, and electrons. 19. What are characteristics of metals? 20. What are characteristics of metalloids? 21. Where are metalloids located? 22. What are characteristics of non-metals? 23. Where are non-metals located? 24. Where are the protons 25. Where are the neutrons Protons have a positive (+) charge, and each has a mass of one atomic mass unit (amu). Neutrons have no charge (sometimes stated as a neutral or zero (Ø) charge), and each also has a mass of 1 amu. 26. Where are the electrons Electrons have a negative (-) charge, and a very tiny mass of amu. The mass of electrons are so small that they are usually ignored when adding up the mass of the entire atom to state the atom s atomic

4 All of the atom s electrons are located somewhere in the electron cloud. It is not possible to know exactly where the electrons of an atom are located. It is useful to think of electrons of orbiting the nucleus much as planets orbit the Sun (as shown in the Bohr Model below), though electrons don t really have separate defined orbits. 27. What determines the identity of an atom? Atoms of a particular element have a set number of protons. For example, every atom of hydrogen has one proton, and every atom of gold has 79 protons. The number of protons is called the element s atomic number. Atoms that are electrically neutral will have the same number of protons and electrons. If an atom has an electrical charge, it is because it has more or less electrons that its fixed number of protons. 28. What causes an atom to have an electrical charge? 29. What determines the atomic mass of an element? The total number of protons and neutrons in an atom s nucleus is called the atomic mass of that atom. Identify the charge of each atom.

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