Chapter2 - Chapter 2 Atoms Molecules and Life Everything in...

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Chapter 2: Atoms, Molecules, and Life Everything in the universe is either matter or energy Matter can be categorized into elements Element:  substance that cannot be broken down or converted to other  substances by ordinary chemical means There are 110 known elements, 92 of which occur in nature The way these elements interact is the basis for the science of chemistry and  some physics Atom:  basic structure of matter made up of smaller subatomic particles. Smallest  subdivision of matter Protons:  positively charged subatomic particle Neutron:  neutrally charged subatomic particle Atomic nucleus:  made of protons and neutrons Electrons:  negatively charged subatomic particle which is lighter than protons or  neutrons that orbit the atomic nucleus  An atom alone has balanced number of electrons and protons therefore being  electrically neutral 92 types of atoms or elements in nature Atomic number:  number of protons in the atomic nucleus, unique for each  element. (atomic #=protons). DOES NOT CHANGE. Isotope:  result when an atom of the same element has a different number of  neutrons Radioactive isotope:  isotope that spontaneously breaks apart forming different  types of atoms and releasing energy in the process. (ex: radioactive isotope of  uranium forms lead) Electron shells:  the different distances that electrons orbit in around the  nucleus. Electrons in different shells have different amounts of energy. Lowest  shell=lowest energy. Electron must absorb or release energy to move from one  level to another First shell can hold 2 electrons, 2 nd  can hold 8 Octet rule:  Atoms tend to gain, lose, or share electrons so that they have 8  electrons in their outermost shell Molecule:  consists of 2+ atoms which can be of the same or different elements.  Atoms are held together by interactions among their outermost electron shells An atom will not react with other atoms when its outermost electron shell is  completely full or empty.  This is described as  inert.
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An atom will react with other atoms when its outermost electron shell is only  partially full. This is described as  reactive. Gaining stability:  atom can lose an electron to empty the outer shell, gain  electrons to fill the outer shell, or share electrons with another atom with both  atoms behaving as if they had full outer shells Chemical bonds:  results of atoms gaining stability. Attractive forces that hold  atoms together in molecules Chemical reactions:  make and break chemical bonds to form new substances Ion:
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