Two or more atoms bonded together are called a molecule. o 2 electrons fill the first shell o 8 electrons fill every other shell

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Magdalene Casey
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3 Atoms aren t alive but they spend their entire existence transitioning from instability to stability. An atom is stable if its outermost shell is filled with electrons. If two atoms are missing electrons in their outer shell, they can react by trading or sharing electrons to reach a filled outer shell o 2 electrons fill the first shell o 8 electrons fill every other shell Two or more atoms bonded together are called a molecule

Covalent bonds are the strongest bonds Covalent bonds occur between two atoms who can share their outer shell s electrons o Even though each atom needs 8 electrons in the outer shell, the total

4 Covalent bonds are the strongest bonds Covalent bonds occur between two atoms who can share their outer shell s electrons o Even though each atom needs 8 electrons in the outer shell, the total number of electrons won t be 16. o Some electrons count towards both atoms Covalent bonds result in all atoms having a completed outer shell and, therefore, are all stable. Because both atoms are stable, they have no need to break their bond. This is why covalent bonds are incredibly strong

6 If both atoms can t be happy and stable, one is better than none Ionic bonds are bonds where one atom borrows another atom s electrons to fill it s outer shell The atom with the completed shell is stable, but the other atom isn t. It will try to break away. o Therefore, ionic bonds are highly reactive. A reaction is the result of two atoms either forming or breaking their bond.

8 The more charges an atom has, the stronger it s overall pull. o Imagine if athletic balls were all magnetic. Which would be stronger, a basketball or a golf ball? When atoms are covalent (they share electrons) but one atom is much stronger than the other, it creates a polar covalent bond o Polar refers to having a positive and negative pole or side The weaker atoms are all pulled to one side of the stronger atom, giving the overall molecule a positive and negative charge. Polar covalent: same as covalent, but when the electrons aren t shared equally creating a molecular charge

10 Polar covalent bonding has an incredibly important side affect. By giving a molecule a positive and negative charge, whole molecules can bond with each other just like magnets These bonds are called hydrogen bonds, because they always involve hydrogen atoms in a polar covalent molecule Hydrogen bonds form quickly and are strong bonds, but can easily be broken by trauma, temperature, or blocking the charges (again, just like a magnet)

12 Water plays a role in building organisms, cycling nutrients, and building ecosystems Every organism is 70-90% water Water cools organisms, helps with transporting nutrients within the body, and provides protection Because of how familiar and numerous it is, almost all reactions use water and water reactions as a reference Pick your reason: you need to be familiar with water

13 Water molecules are polar covalent. Each oxygen in water (the negative charge of the molecule) forms a hydrogen bond with a hydrogen (positive charge) of a different water molecule This allows for the following properties of water: 1. Heat capacity: water can store hundreds of calories of energy within every hydrogen bond o It takes longer to heat/cool water than solids or gasses 2. Universal Solvent: water breaks apart molecules by using it s charges to bond with charges of other polar molecules o NaCl Sodium (Na) is positively charged. Chlorine (Cl) is negatively charged. o By breaking these elements, the salt dissolves into the water

15 3: Cohesion/Adhesion. Water molecules can bond to each other and to other objects o Water flows freely and changes forms without breaking up o This makes water excellent for transport 4: Surface Tension o Hydrogen bonds form a hammock on the surface of water o Organisms can float if they do not break these bonds 5: Capillary Action o Water can move against gravity by piggybacking itself 6: Density o Water is unique because it is less dense as a solid than as a liquid, so ice will float on water o Life exists below frozen lakes because of this

20 Acids are solutions with high concentrations of hydrogen ions o In the presence of water, an acidic molecule will break apart and form hydrogen ions o HCl H + + Cl - Bases are solutions with high concentrations of hydroxide (OH - ) ions o In the presence of water, a basic molecule will break apart and form hydroxide ions o NaOH Na + + OH - An ion is an atom or molecule that has a positive or negative charge because its protons and electrons are unequal.

21 We measure acids and bases using the ph scale It is important to measure the acidity or basic level of substances Too strong of acids or bases are dangerous, even deadly, to most organisms. 7 is neutral. Water has a ph of 7 The further from 7 you get, the stronger the acid/base A ph of is acidic A ph of is basic

THE CHEMISTRY OF LIFE

THE CHEMISTRY OF LIFE ATOMS All living things are made up of matter Atoms are the smallest unit of matter Made up of 3 subatomic particles: 1. Protons- positively charged, found in the nucleus, has mass