Chemistry Refresher & Water Mr. Perez

Before we begin, let’s see what you remember… On the periodic table of elements, the number above the element’s abbreviation (atomic number) counts the number of _________ the element contains. Electrons Protons Neutrons Doughnuts # of protons

Contd. Carbon, hydrogen, oxygen and ____________ make up 96% of living matter. Helium Nitrogen Boron Potassium Nitrogen

Contd. ____________ bonds are formed when two atoms share a pair of valence electrons. Ionic Hydrogen Covalent Double Covalent

Contd. TRUE or FALSE If an element has 10 electrons, its electron distribution will have 2 electrons in the first valence shell and 8 in the second valence shell. True

Matter & Elements Organisms are composed of matter, or anything that takes up space and has mass Matter is made up of elements, substances that cannot be broken down to other substances by chemical reactions

Compounds Sodium (Na) + Chlorine (Cl) = Table Salt (NaCl) Compounds are made up of two or more elements and have characteristics different from the elements that make it up Sodium (Na) + Chlorine (Cl) = Table Salt (NaCl)

Elements of Life Carbon, Hydrogen, Oxygen, and Nitrogen make up 96% of living matter REMEMBER: CHON = LIFE The other 4% of living matter is made up of trace elements such as potassium, calcium, phosphorous and sulfur.

Structure of atoms Atoms are made up of: The structure of atoms that makes up an element allows it to have certain properties Atoms are the smallest units of matter that still retain the properties of an element Atoms are made up of: Protons (+) = atomic mass Neutrons (0) Electrons (-)

An Element’s Energy level An element’s energy level depends on the distribution of valence electrons Valence electrons are the electrons found in the outermost shell Full shells are less reactive than those that are empty or missing a few electrons

Hydrogen 1H 2 He 4.00 Atomic number Helium 2He Mass number First shell Figure 2.9 Hydrogen 1H 2 He 4.00 Atomic number Helium 2He Mass number First shell Element symbol Electron distribution diagram Lithium 3Li Beryllium 4Be Boron 5B Carbon 6C Nitrogen 7N Oxygen 8O Fluorine 9F Neon 10Ne Second shell Sodium 11Na Magnesium 12Mg Aluminum 13Al Silicon 14Si Phosphorus 15P Sulfur 16S Chlorine 17Cl Argon 18Ar Third shell

Chemical Bonds Atoms with incomplete valence shells can share or transfer electrons with other atoms Chemical bonds keep them together Covalent bonds involve the sharing of electrons Single bonds is the sharing of one pair of electrons Double bonds is the sharing of two pairs of electrons Ionic bonds involve the loss or gain of an electron Cation= + charged ion Anion = - charged ion

Molecules Molecules are formed by two or more atoms held together by covalent bonds We use structural formulas to represent atoms that are bonded together For example H—H, which can also be written H2 Compounds are formed when two or more different elements combine

Figure 2.12 Name and Molecular Formula Electron Distribution Diagram Lewis Dot Structure and Structural Formula Space- Filling Model (a) Hydrogen (H2) (b) Oxygen (O2) (c) Water (H2O) (d) Methane (CH4)

Weak chemical bonds STRONG = COVALENT WEAK = IONIC & HYDROGEN These weak bonds help retain shapes

Hydrogen bonds Hydrogen bonds are formed when a hydrogen atom is covalently bonded to an electronegative atom and is attracted to another electronegative atoms Usually, the electronegative partners are oxygen or nitrogen Electronegativity is an atom’s attraction for electrons in a covalent bond The stronger the electronegativity the more electrons will be pulled to itself when sharing

Crash Course https://www.youtube.com/watch?v=QXT4OVM4vXI

Water, Water, Every Where!!! Properties of Water The Versatile Molecule

Expanding Upon Freezing What if this did not occur? Allows ice to float and stops lakes and rivers from freezing solid (insulation).

II. Water Molecule Water is made up of Hydrogen and Oxygen Oxygen has 6 electrons and high electronegativity Hydrogen has 1 electron and low negativity Each water molecule has two polar covalent bonds, giving it partial positive and negative regions

II. Water Molecule C. This molecule H₂O is neutral (10 e⁻& 10 p⁺) However there is more to this story... D. Polarity: an uneven distribution of electrons between two atoms 1. Oxygen atom in water has a stronger attraction to the electrons than hydrogen 2. Water is a bent molecule so the oxygen end is slightly negative while the hydrogen end is slightly positive

III. Hydrogen Bond A. Since polar molecules have a slightly charged end they are attracted one another 1. Slightly positive is written: (+) 2. Slightly negative is written: (-) B. The bonding between the polar water molecules, from one oxygen to a hydrogen is a hydrogen bond Hydrogen bonds are weak bonds but collectively together they are strong!

IV. Cohesion & Adhesion Adhesion Cohesion A. The ability of water to form multiple hydrogen bonds gives it unique properties 1. Cohesion: attraction between molecules of the same substance i.e. drops of water form beads on a flat surface (high surface tension) 2. Adhesion: attraction between molecules of a different substance i.e. meniscus in a graduated cylinder and why water flows through a plant (capillary action) Adhesion Cohesion

V. Solutions & Suspensions Water is not always pure A. Mixture: material composed of two or more elements or compounds that are physically mixed together i.e. salt water, salt & pepper, atmosphere B. Two types of mixtures that can be made with water Solutions: all components are evenly distributed Suspensions: mixtures with nondissolved material and separate pieces

VI. Heat Capacity A. Water has a high specific heat. In other words it takes a lot of energy to raise water just by 1 degree. B. This allows organisms that not only live in water but others that are mostly made up of water to maintain a constant body temperature.

VII. Good Solvent Because water is polar, it bonds to ions and polar molecules. Even very small non-polar molecules, for example CO2 dissolve. Remember, LIKE dissolves LIKE Hydrophobic dissolved hydrophobic

Hydrogen Bonds & Pennies Water molecules are polar because there is an uneven of electrons between the oxygen and hydrogen atoms. This causes one end of one water molecule to be attracted to another water molecule. This process is cohesion! Lets test how strong these cohesion forces are by placing drops of water on a penny until the cohesive forces break Hypothesis: If I place a max of ____ drops of water onto a penny, then the cohesive forces of water will break and water will spill onto the towel Each person will conduct 2 trials and find the average. What’s the IV, DV, Control?