Chapter 2 Elements and Compounds 2 1 Chapter 2 Elements and Compounds Chapter 2 2 1 The Structure of the Atom 2 2 Elements and the Periodic Table 2 3 Covalent Compounds 2 4 Ions and Ionic Compounds Chapter In Context As we learned in Chapter 1 each of the 116 known elements is composed of a unique type of atom In this chapter we discover that there are actually a number of different variations or isotopes of the atom associated with each element We explore the structure of the atom in further detail and learn how different isotopes are formed We also discuss the different ways that molecules and compounds are represented and named Atoms make up all the matter around us so an understanding of atoms and particularly how we can manipulate atoms to affect their properties has led to numerous benefits in science and in our everyday lives Biology Over the last sixty years since we began to synthesize new elements in the laboratory synthetic isotopes have found significant use in medicine For example when compounds containing the synthetic isotope technetium are injected into patients portions of the body such as the brain the heart and the circulatory system can be imaged Chapter Goals Recognize the components of an atom Describe the organization of the periodic table Identify covalent compounds and their properties Understand the relationship between atoms and ions Identify ionic compounds and their properties Chapter 2 Elements and Compounds 2 2 2 1 The Structure of the Atom OWL Opening Exploration 2 1 Atoms the smallest unit of matter consist of three subatomic particles protons neutrons and electrons A proton carries a relative charge of 1 and has a mass of 1 672622 10 24 g A neutron carries no electrical charge and has a mass of 1 674927 10 24 g An electron carries a relative charge of 1 and has a mass of 9 109383 10 27 g Two of the subatomic particles protons and neutrons are found in the atomic nucleus a very small region of high density at the center of the atom Electrons are found in the region around the nucleus As you will see when we study atomic structure in more detail in an upcoming chapter the precise location of electrons is not determined Instead we visualize an electron cloud surrounding the nucleus that represents the most probable location of electrons Figure 2 1 Note that the atom represented in Figure 2 1 is not drawn to scale In reality electrons account for most of the volume of an atom and the nucleus of an atom is about one ten thousandth 1 10 000 the diameter of a typical atom For example if you expand an atom so that it has a diameter the same size as a football field 100 yards or about 90 meters the nucleus of the atom would have a diameter of only about 1 cm Flashforward Chapter 7 Atomic Structure Figure 2 1 The arrangement of subatomic particles in an atom not drawn to scale The mass and charge of an atom affects the physical and chemical properties of the element and the compounds it forms As shown in Table 2 1 the three subatomic particles are easily differentiated by both charge and mass Table 2 1 Properties of Subatomic Particles Actual mass kg Relative mass Mass u 1 672622 10 27 1836 1 007276 Neutron n 1 674927 10 27 1839 1 008665 9 109383 10 31 1 Proton p Electron e 5 485799 10 4 Actual charge C 1 602 10 19 C 0 0 1 0 19 1 602 10 The mass of an atom is almost entirely accounted for by its dense nucleus of protons and neutrons The actual mass of protons and neutrons is very small so it is more convenient to define the mass of these particles using a different unit The atomic mass unit u is defined as one twelfth of the mass of a carbon atom that contains 6 protons and 6 neutrons Because neutrons and protons have very similar masses both have a mass of approximately 1 u The mass of an electron is about 2000 times less that of protons and neutrons and it has a mass of approximately zero on the atomic mass unit scale Putting together all of this information we can now represent a typical atom more accurately as shown in Figure 2 2 Relative charge C 1 Figure to come Figure 2 2 Diagram of a carbon atom Chapter 2 Elements and Compounds 2 3 Atoms are neutral because protons and electrons have equal opposite charges and atoms have equal numbers of positively charge protons and negatively charged electrons An ion is an atom with an unequal number of protons and electrons which therefore carries an overall positive or negative charge When an atom carries more protons than electrons it carries an overall positive charge and is called a cation An atom with more electrons than protons has an overall negative charge and is called an anion As you will see later in this chapter ions have very different properties than the elements they are derived from Atomic Number Mass Number and Atomic Symbols Atoms of each element can be distinguished by the number of protons in the nucleus The atomic number Z of an element is equal to the number of protons in the nucleus For example the carbon atom shown in Figure 2 2 has six protons in its nucleus and therefore carbon has an atomic number of six Z 6 Each element has a unique atomic number and all atoms of that element have the same number of protons in the nucleus All atoms of hydrogen have one proton in the nucleus Z 1 and all atoms of gold have 79 protons in the nucleus Z 79 Because protons carry a positive charge 1 in a neutral atom the atomic number also equals the number of electrons 1 in that atom An atom can also be characterized by its mass Because the mass of electrons is negligible the mass of an atom in atomic mass units u is essentially equal to the number of protons and neutrons in the nucleus of an atom called the mass number A For example a carbon atom with 6 protons and 6 neutrons in its nucleus has a mass number of 12 A 12 and a gold atom with 79 protons and 119 neutrons in its nucleus has a mass number of 198 A 198 The atomic symbol for an element consists of the one or two letter symbol that represents the element along with the atomic number in subscript and the mass number in superscript Figure 2 3 For example the atomic symbol for a carbon C atom with 6 protons and 6 neutrons is 126 C and the symbol for a gold Au atom with 79 protons and 119 neutrons is 198 79 Au Note that the number of neutrons in an atom is equal to the difference between the mass number and the atomic number Chapter Goals Revisited Recognize the components of an atom Write atomic symbols mass …