CH 2 OUTLINE 11e.pptx - CHAPTER 2 Atoms Molecules and Life...

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CHAPTER 2 Atoms, Molecules, and Life
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Atoms are the fundamental structural units of matter and composed of 3 particles In the nucleus, positively charged protons and uncharged neutrons Orbiting around the nucleus, negatively charged electrons Atoms are electrically neutral because of the # of protons and # electrons The number of protons in the nucleus of an atom is known as the atomic number The atomic mass of an element is the total mass of its protons, neutrons, and electrons 2.1 What are Atoms?
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Atomic Models e electron shell e p p p n atomic nucleus a) Hydrogen (H ) 1 proton n e (b) Helium (He) 2 protons 2 neutrons
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Elements and isotopes An element is a substance that cannot be broken down by ordinary chemical reactions All atoms belong to one of 92 types of naturally occurring elements An atomic number (number of protons) is the defining value for an element All atoms of an element have the same atomic # Example: carbon has six protons, nitrogen has seven
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Top six 6 elements humans are composed of
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Elements and isotopes (continued) However, atoms of an element may vary in the number of neutrons they have in the nucleus Variant atomic forms of an element are called isotopes Some isotopes are radioactive (meaning that they spontaneously break apart and form different atoms At room temperature, elements may occur as solids, liquids or gases
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Carbon (C) Oxygen (O) Phosphorus (P) Calcium (Ca) Ca O C P 4 e 6 e 5 e 2 e 8 e 8 e 8 e 2 e 2 e 2 e 2 e 6 p 8 p 15 p 20 p 6 n 8 n 16 n 20 n Electron shells LARGER atoms can accommodate more electron than smaller ones can Electrons are distributed around the nucleus of an atom in electron shells The first shell, or energy level holds 2 electrons The second shell holds up to 8 electrons
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Electron shells (continued) The roles of the nucleus and the electrons are: Nucleus stability Electrons interact with other atoms (for example to form a chemical bond) Chemical bonds are the force of attraction between atoms that holds them together Many different types of chemical bonds
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Energy capture and release Life depends on electrons Electron shells When energy excites an atom, the electrons jump from Later, the electron falls back into
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2.2 How Do Atoms Interact to Form Molecules? Interaction between atoms Molecules consist of two or more atoms, from same or different elements A substance made of atoms of different elements is a compound Reactions between atoms depend upon the configuration of electrons in the outermost electron shell
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Interaction between atoms (continued) Atoms will not react with other atoms if the
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