Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Cecie Starr Christine Evers Lisa Starr www.cengage.com/biology/starr Chapter 2 Life’s Chemical Basis (Sections 2.1 - 2.3) Albia Dugger • Miami Dade College 2.2 Start With Atoms • At life’s first level of organization, atoms interact with other atoms to form molecules • The properties of molecules depend on, but differ from, those of their atomic components • The behavior of elements, which make up all living things, depends on the structure of individual atoms Key Terms • atom • Particle that is a fundamental building block of all matter • element • A pure substance that consists only of atoms with the same number of protons Structure of an Atom • Atoms consist of electrons (negative charge) moving about a nucleus of protons (positive charge) and neutrons (uncharged) Key Terms • nucleus • Core of an atom; occupied by protons and neutrons • proton • Positively charged subatomic particle that occurs in the nucleus of all atoms • neutron • Uncharged subatomic particle in the atomic nucleus Key Terms • charge • Electrical property • Opposite charges attract, and like charges repel • electron • Negatively charged subatomic particle that occupies orbitals around an atomic nucleus Elements • The number of protons in the nucleus defines the element • The periodic table lists elements in order of atomic number • Elements in columns behave in similar ways Key Terms • atomic number • Number of protons in the atomic nucleus; determines the element • periodic table • Tabular arrangement of known elements by atomic number The Periodic Table ANIMATION: Electron distribution Isotopes • Isotopes are atoms of an element that differ in mass number • isotopes • Forms of an element that differ in the number of neutrons their atoms carry • mass number • Total number of protons and neutrons in the nucleus of an element’s atoms Radioisotopes • Atoms of radioisotopes spontaneously emit subatomic particles or energy by the process of radioactive decay, which can transform one element onto another • Researchers use radioisotopes to make tracers that track biological processes inside living organisms Key Terms • radioisotope • Isotope with an unstable nucleus • radioactive decay • Process by which atoms of a radioisotope emit energy and/or subatomic particles when their nucleus spontaneously disintegrates • tracer • Molecule labeled with a detectable substance Key Concepts • Atoms and Elements • Atoms, the building blocks of all matter, differ in their numbers of protons, neutrons, and electrons 2.3 Why Electrons Matter • Atoms acquire, share, and donate electrons • Whether an atom will interact with other atoms depends on how many electrons it has • A typical atom has the same number of electrons as protons Shell Models • Shell models help us visualize how electrons populate atoms from the innermost shell outward • Concentric circles represent successive energy levels • 1st shell: up to 2 electrons • 2nd shell: up to 8 electrons • 3rd shell: up to 8 electrons Shell Models A The first shell corresponds to the first energy level, and it can hold up to 2 electrons. Hydrogen has one proton, so it has 1 electron and 1 vacancy. A helium atom has 2 protons, 2 electrons, and no vacancies. The number of protons in each model is shown. B The second shell corresponds to the second energy level, and it can hold up to 8 electrons. Carbon has 6 protons, so its first shell is full. Its second shell has 4 electrons, and four vacancies. Oxygen has 8 protons and two vacancies. Neon has 10 protons and no vacancies. first shell second shell C The third shell, which corresponds to the third energy level, can hold up to 8 electrons. A sodium atom has 11 protons, so its first two shells are full; third shell the third shell has one electron. Thus, sodium has seven vacancies. Chlorine has 17 pro tons and one vacancy. Argon has 18 protons and no vacancies. 1 proton 1 1 electron hydrogen (H) 2 helium (He) 6 8 carbon (C) oxygen (O) 11 17 sodium (Na) chlorine (Cl) 10 neon (Ne) 18 argon (Ar) Stepped Art Fig. 2.5, p. 26 ANIMATION: Shell models of common elements To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Atoms and Ions • An atom is most stable when it has no vacancies • Atoms fill vacancies by gaining or losing electrons, or by sharing electrons with other atoms • An atom with a different number of electrons and protons carries a charge, and is called an ion Swapping Electrons • Electronegativity is a measure of how strongly an atom attracts electrons from other atoms • An atom that gains an electron is a negative ion • An atom that loses an electron is a positive ion Ion Formation electron gain electron loss Ion Formation Chlorine atom 17p+ 17e– _________ charge: 0 Sodium atom 17 11 Chlorine ion 17p+ 18e– ___________ charge: –1 11p+ 11e– __________ charge: 0 Sodium ion 17 A A chlorine atom (Cl) becomes a negatively charged chloride ion (Cl–) when it gains an electron and fills the vacancy in its third, outermost shell. 11 11p+ 10e– _________ charge: +1 B A sodium atom (Na) becomes a positively charged sodium ion (Na+) when it (Cl–) when it gains an electron loses the electron in its third shell. The atom’s full second shell is now its outermost, so it has no vacancies. Fig. 2.6, p. 27 electron gain Ion Formation Chlorine atom 17p+ 17e– _________ charge: 0 17 Chlorine ion 17p+ 18e– ___________ charge: –1 17 A A chlorine atom (Cl) becomes a negatively charged chloride ion (Cl–) when it gains an electron and fills the vacancy in its third, outermost shell. Fig. 2.6a, p. 27 electron loss Ion Formation Sodium atom 11 11p+ 11e– __________ charge: 0 Sodium ion 11 11p+ 10e– _________ charge: +1 B A sodium atom (Na) becomes a positively charged sodium ion (Na+) when it (Cl–) when it gains an electron loses the electron in its third shell. The atom’s full second shell is now its outermost, so it has no Fig. 2.6b, p. 27 electron gain electron loss Ion Formation Chlorine atom 17p+ 17e– _________ charge: 0 Sodium atom 17 11 Chlorine ion 17p+ 18e– ___________ charge: –1 11p+ 11e– __________ charge: 0 Sodium ion 17 A A chlorine atom (Cl) becomes a negatively charged chloride ion (Cl–) when it gains an electron and fills the vacancy in its third, outermost shell. 11 11p+ 10e– _________ charge: +1 B A sodium atom (Na) becomes a positively charged sodium ion (Na+) when it (Cl–) when it gains an electron loses the electron in its third shell. The atom’s full second shell is now its outermost, so it has no vacancies. Stepped Art Fig. 2.6, p. 27 ANIMATION: Ionic bonding To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE Key Terms • shell model • Model of electron distribution in an atom • ion • Charged atom • electronegativity • Measure of the ability of an atom to pull electrons away from other atoms Sharing Electrons • A chemical bond is an attractive force that unites two atoms as a molecule • A compound is a molecule that consists of two or more elements • A mixture is an intermingling of substances Key Terms • chemical bond • An attractive force that arises between two atoms when their electrons interact • molecule • Group of two or more atoms joined by chemical bonds Key Terms • compound • Type of molecule that has atoms of more than one element • mixture • An intermingling of two or more types of molecules • A liquid mixture is a solution Key Concepts • Why Electrons Matter • How an atom interacts with other atoms depends on the number and arrangement of its electrons ANIMATION: The shell model of electron distribution To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE ANIMATION: How atoms bond To play movie you must be in Slide Show Mode PC Users: Please wait for content to load, then click to play Mac Users: CLICK HERE