O helium has a very stable outer shell and cant be

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o Helium has a very stable outer shell and can’t be lit on fire - If an atom has a vacancy in the outer electron shell, it will try to fill that vacancy or get rid of the “extra” electrons so the outer shell is full o Things move to the path of least resistance o Ex: Sodium and Chlorine Na needs to lose an electron Cl needs to gain an electron o These electrons are matter. Matter can’t be created or destroyed. So these electrons can’t just go away. It has to either be given or gained. - A reactive atom will try to fill the valence shell by interacting with other atoms - This interaction may result in two atoms forming a chemical bond o A chemical bond is an attraction that holds two atoms together o A molecule is two or more atoms held together by chemical bonds - The smallest unit that retains the physical and chemical properties of a compound o Similar atoms/molecule = element o Different atoms/molecules = compound - If an atom has almost empty or an almost full outer electron hell is likely to form an ion o An ion is charged atom or molecule. it is charged because it has either lost or gained electrons o An anion is a negatively charged atom or molecule. It has gained an electron. o A cation is positively charged atom or molecule. It has lost an electron. When Na loses an electron, it has a positive charge When it gains an electron, it has a negative charge - A covalent bond is a bond formed when two atoms share pairs of electrons o Share electrons; electrons are moving between atoms and this satisfies both atoms involved. o Nonpolar covalent bond is equal sharing; it is a covalent bond in which the sharing of the electron pair is equal Opposite charges attract Ex: hydrogen One hydrogen atom with positive charge and another hydrogen atom with a positive charge. They are sharing electrons in the middle because they have a negative charge and OPPOSITES ATTRACT. o Polar covalent bond is a covalent bond in which the sharing of the electron pair is unequal This is because not all atoms have the same charge The bigger the atom, the stronger it is and it will pull more. Ex: water
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5 These bonds are responsible for giving water all its unique qualities. Water is extremely polar 2 of the electrons on the hydrogen atom will share with the oxygen atoms. Even though these electrons are being shared, they will be closer to the hydrogen nucleus than to the oxygen nucleus. This makes is a polar bond. If these electrons are closer to hydrogen than oxygen, hydrogen takes on a partial negative charge All the hydrogens have a slightly negative charge and all the oxygen have a slightly positive charge - Electronegativity o Defined as an atom’s ability to attract and hold electrons. An indication of how much positive charge is in the nucleus. Assigned a numerical value. The higher the #, the more electronegative an atom is Basically, how strong is the atom Takes a lot of energy to take away electrons o Body is made of vast majority of hydrogen, carbon, nitrogen and oxygen Hydrogen = 2.2
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