What Are Atoms Made Of - Answer Key 2

Hint 5. Determine the number of valence electrons for Xe How many valence electrons are in an atom of the element Xe? Express your answer as an integer. ANSWER: 8 Hint 6. Determine the valence electron trend For the main group elements, how does the number of valence electrons change across a period as you move from left to right? ANSWER: increases. The number of valence electrons decreases. stays the same. ANSWER: Reset Xe Br Sb In Help Rb Correct The number of valence electrons increases within a period from left to right for the main group elements. Item 7 Electrons are located in a large volume of space surrounding the nucleus. This space contains different energy levels that electrons fill in order from lowest to highest in energy, and each energy level contains one or more sublevels where electrons with identical energy are found. An electron configuration is a notation used to indicate the placement of an atom's electrons in these sublevels in order of increasing energy. The configuration is written by listing the sublevels occupied by electrons from lowest to highest in energy, and by indicating how many electrons occupy each sublevel by using exponents. The sublevels, from lowest to highest in energy, are identified by the letters s , p, d, and f. Since the periodic table is arranged by the number of protons in each atom (and electrons if the atom is neutral), the sublevels form blocks in the periodic table: Energy levels depend upon what period the element resides in. If n is the period number the element resides in, 1. 2. 3. 4. The energy The energy The energy The energy level for s sublevels is the same as the period number (n). level for p sublevels is the same as the period number (n). level for d sublevels is one less (n – 1) than the period number. level for f sublevels is two less (n – 2) than the period number. Specific sublevels are described listing the value of the energy level followed by the type of sublevel. For example, 3p is a p sublevel of the third energy level. Part A When writing a complete electron configuration, you write the filled sublevels in order first, and then if there is a partially filled sublevel, you write it last in the sequence. You can identify the last sublevel containing electrons by finding the element in the periodic table, and determining which block and sublevel the element corresponds to. Identify the last occupied sublevel, which can be completely or partially filled, for each of the following elements. Drag the appropriate items to their appropriate bins. Hint 1. How to approach the problem Identifying the last occupied sublevel (filled or partially filled) of an element involves two steps: 1. Locate which block the element resides in on the periodic table (s , p, d, or f). 2. Identify which period, or row, of the periodic table the element resides in (1-7). If n is the period number the element resides in, 1. The energy 2. The energy 3. The energy 4. The energy level for s sublevels is the same as the period number (n). level for p sublevels is the same as the period number (n). level for d sublevels is one less (n – 1) than the period number. level for f sublevels is two less (n – 2) than the period number. For example, yttrium ( ) resides in the fifth period and in the d block of the periodic table. The last partially filled sublevel of yttrium is 4d. Hint 2. Identify which elements have their final electrons either filling or partially filling a sublevel of the fourth energy level Which of the following elements have their final electrons either filling or partially filling a sublevel of the fourth energy level? Check all that apply. ANSWER: Hint 3. Determine which block each element resides in on the periodic table Sort each element into the block it resides in on the periodic table. Use the periodic table below or in the Resources menu as a guide. Drag the appropriate items to their appropriate bins. ANSWER: Reset Help ANSWER: Reset Help Correct Finding the last occupied sublevel of an element requires locating it on the periodic table, understanding where each block resides, and understanding how sublevels relate to the periods of the periodic table for each block. Abbreviated electron configurations Abbreviated electron configurations use a bracketed chemical symbol (to represent the electron configurations) of a noble gas (group 8A or 18) as the starting point for an electron configuration for an element in the next row after whichever noble gas is chosen. For example, the abbreviated electron configuration for scandium would be as opposed to . Part B Match each complete or abbreviated electron configuration with the element it corresponds to, assuming that each configuration is for a neutral atom. Drag the appropriate items to their appropriate bins. Hint 1. How to approach the problem There are two methods for identifying an element based on a given electron configuration. One is to locate the last occupied sublevel and count down the period the correct number of electrons. For example, the last occupied block sublevel for the electron configuration is the 4s sublevel. Since the exponent following 4s is 1, then the first element in this sublevel block is the element matching this electron configuration. In this case, the element is potassium ( ). The second method involves adding the electrons represented by the exponents in the electron configurations. For example, the electron configuration displays 8 electrons (2 + 2 + 4 = 8). Thus, this electron configuration corresponds to the element with an atomic number of 8, oxygen ( ). For abbreviated electron configurations, add the exponents to the atomic number of the noble gas being referenced. For example, the electron configuration has 10 + 2 + 5 = 17 electrons. The element corresponding to this electron configuration is chlorine ( ). Hint 2. Determine how many electrons are represented in an electron configuration How many electrons are represented by the following electron configuration: ? ANSWER: 4 36 16 52 Hint 3. Determine which group the element each electron configuration specifies should fall under Groups are the columns of the periodic table. They are numbered 1-18 starting with the s orbitals, moving through the transition metals, and ending with the p orbitals. For example, given the electron configuration , the last orbital filled is the 2s orbital and it has two electrons. Therefore, given that there are only two electrons in the valence shell, the element must be in group 2 of the periodic table. On the other hand, the electron configuration would correspond to an element in group 13. The d block, groups 3-12, comes between the s and p blocks. Sort each electron configuration into the group (column) on the periodic table that contains the element it represents by using the last orbital filled with electrons. Drag the appropriate items to their appropriate bins. ANSWER: Reset ANSWER: Help Reset Help Correct There are two ways to identify an element being represented by an electron configuration. One is to locate the last occupied sublevel on the periodic table and count down the period the correct number of electrons. The other is to calculate the atomic number by adding up the electrons represented by the exponents (and the atomic number of the noble gas being referenced for abbreviated electron configurations). Element Electron Configuration Silicon ( ) Bismuth ( ) Niobium ( ) Tellurium ( Zinc ( ) ) Magnesium ( ) Part C Write the complete electron configuration for gallium using the periodic table. Express your answer in complete form, in order of increasing orbital. For example, would be entered as 1s^22s^2. Hint 1. How to approach the problem The following is a guide to writing electron configurations using sublevel blocks: 1. Locate the element on the periodic table. 2. Write the filled sublevels in order, going across each period. 3. Complete the configuration by counting the electrons in the last occupied sublevel block. Hint 2. Determine the order in which the sublevels are filled Rank the following sublevels in the order that they are filled from first to last. Rank the sublevels from first to last in terms of the order they are filled. ANSWER: Reset 1s 2s 2p 3s 3p 4s 3d Help 4p The correct ranking cannot be determined. Hint 3. Determine how many electrons are in the last occupied sublevel How many electrons are present in the last occupied sublevel of gallium? Express your answer numerically. ANSWER: Number of electrons in the last occupied sublevel = 1 ANSWER: Electron configuration: 1s^22s^22p^63s^23p^64s^23d^10 Correct The complete electron configuration for gallium is . Notice that the 4s sublevel is completely filled before the 3d sublevel begins to be filled. Chromium and copper are exceptions. Chromium places 1 electron in the 4s sublevel and 5 electrons in the 3d sublevel to produce two half-filled sublevels, which are particularly stable. Copper places 1 electron in the 4s sublevel and 10 electrons in the 3d sublevel to produce a halffilled s sublevel and a completely filled d sublevel. Half-filled and filled sublevels are energetically more stable, which is why the exceptions are observed. Item 8 An electron-dot symbol consists of the symbol for an element surrounded by dots. The number of dots indicates the number of valence electrons in an atom of that element. Dots are placed on four sides of the symbol (top, bottom, left, and right) with a maximum of two per side. Also keep in mind that the electrons should be as spread out as possible. For example, correct and incorrect ways of writing the electron-dot symbols for oxygen are shown here. Correct Incorrect In the correct electron-dot symbol, the electrons are distributed across all sides. Part A Add single electrons and/or electron pairs as needed to complete the electron-dot symbol for astatine, . To return the atom to its original state, use the reset button. Click to select an electron-pair or single electron, then click on the element symbol to add electrons. Click the reset button to clear all electrons and start over. Hint 1. Determine the number of valence electrons in an astatine atom Considering that astatine, , is in group 7A of the periodic table, how many valence electrons does an atom of Express your answer as an integer. Hint 1. How to find the number of valence electrons have? One way to determine the number of valence electrons is to look at the electron configuration. Valence electrons are those in the outermost shell of an atom. To determine the number of valence electrons in an atom, it helps to look at the electron configuration. The electron configuration of astatine is . The outermost shell in this case is the sixth shell, and so the valence electrons are those in the 6s and 6p subshells. Notice that the 6s subshell contains two electrons, and the 6p subshell contains five electrons. Another way to determine the number of valence electrons is to notice the trend in the electron configurations of the elements within a group in the periodic table. For example, elements in groups 1A, 2A, 3A, and 4A have one, two, three, and four valence electrons, respectively. Following this same trend, how many electrons does a group 7A element have? ANSWER: 7 ANSWER:             At   Correct Part B Add single electrons and/or electron pairs as needed to complete the electron-dot symbol for , a generic element from group 4A of the periodic table. Click to select an electron-pair or single electron, then click on the element symbol to add electrons. Click the reset button to clear all electrons and start over. Hint 1. Determine the number of valence electrons for group 4A elements How many valence electrons does an atom of a group 4A element have? Express your answer as an integer. Hint 1. How to find the number of valence electrons Valence electrons are those in the outermost shell of an atom. To determine the number of valence electrons in an atom, it helps to look at the electron configuration. If you were to look at the electron configurations of the elements in the same group, you would notice a trend. For example, elements in groups 1A, 2A, and 3A have one, two, and three valence electrons, respectively. Following this same trend, how many electrons does a group 4A element have? ANSWER: 4 ANSWER:             X   Correct This symbol could represent any group 4A element because carbon, silicon, germanium, tin, and lead atoms all have four valence electrons. Item 9 Use the periodic table to identify the elements with the following mass numbers and neutron counts. You may want to reference (Page) Section 2.4 while completing this problem. Part A = 186, with 111 neutrons Express your answer as a chemical symbol. ANSWER: Correct The mass number ( ) is the total number of protons and neutrons in an atom, whereas the atomic number ( ) is the number of protons: From the above two formulas we get This formula is used to identify the atomic symbol if the mass number and number of neutrons are known. On rearranging the above equation, we find The periodic table is used to identify the element for the calculated atomic number. Given = 186, with 111 neutrons, the equation would be By using the periodic table, you can correlate the atomic number to the element that contains 75 protons in the nucleus. Part B = 129, with 75 neutrons Express your answer as a chemical symbol. ANSWER: Correct Part C = 48, with 26 neutrons Express your answer as a chemical symbol. ANSWER: Correct Since that mass number ( ) is the sum of the number of protons plus neutrons in the nucleus of an atom, subtracting the number of neutrons from this value will give you the number of protons in the atom: The periodic table is used to identify the element for the calculated atomic number. Given = 48, with 26 neutrons, the equation would be By using the periodic table, you can will find that cell 22 in the table is Ti. Item 10 An element used to sanitize water supplies has two naturally occurring isotopes with mass numbers of 35 and 37, and 17 electrons. Write the symbols for both isotopes, including their atomic numbers and mass numbers. Part A Complete the isotope symbol with mass numbers of 35. Express your answer as an isotope. ANSWER: Correct Part B Complete the isotope symbol with mass numbers of 37. Express your answer as an isotope. ANSWER: Correct Item 11 Part A Identify the following elements as metals, nonmetals, or metalloids. Drag the appropriate items to their respective bins. ANSWER: Reset K Mg Se Ar Correct Item 12 Part A Locate aluminum in the periodic table and give its group number. ANSWER: 3A Correct Part B Give its period number. ANSWER: 3 Ge Sb Help