Water Notes_Unit 1_OCR PDF

1.2 Particle theory and bonding 1 1.2 Objectives 5. Explain the changes of state in water, between solid, liquid and gas, in terms of the kinetic particle theory 6. Describe the structure of the atom, including the nucleus containing protons and neutrons, su...

1.2 Particle theory and bonding 1 1.2 Objectives 5. Explain the changes of state in water, between solid, liquid and gas, in terms of the kinetic particle theory 6. Describe the structure of the atom, including the nucleus containing protons and neutrons, surrounded by electrons arranged in shells 7. Understand that sea water is a mixture of different elements and compounds 8. Describe (including through the use of diagrams) the covalent bonding in a water molecule, limited to the sharing of electron pairs between atoms 9. Identify (including from diagrams) covalent molecules, including water, carbon dioxide, oxygen, sulfur dioxide and glucose 10. Describe (including through the use of diagrams) the ionic bonding in sodium chloride, limited to the loss and gain of electrons to form ions and the subsequent attraction between positive and negative ions 11. Identify (including from diagrams) ionic substances, including sodium chloride and calcium carbonate 12. State the chemical name and formula of salts found in seawater, including sodium chloride (NaCl), magnesium sulfate (MgSO4) and calcium carbonate (CaCO3) 13. Explain the formation of hydrogen bonds in water 14. Explain how hydrogen bonding in water affects the properties of water, limited to solvent action, density, and specific heat capacity 2 Kinetic Particle Theory 3  Kinetic Particle Theory A state of matter is one of the distinct forms in which matter can exist, such as solids, liquids, and gases. The Kinetic Particle Theory explains that: Matter is made up of particles (small pieces) These particles are in CONSTANT motion This motion gives them energy We can measure the average energy of the particles with temperature. The energy level (temperature) of a substance determines what state of matter it is in. ○ Different substances are in different states at different temperatures 4  Solids Particles are held together into an orderly (crystalline) or irregular (amorphous) structure. Low temperature, lowest energy phase 5  Liquids Particles are loosely held together. Higher temperature than solids, lower than gases. 6  Gases No connection between particles. Particles are in constant, random motion Higher temperatures that solids and liquids. 7 Comparison between states of matter 8  Changing States of Matter (Phase Changes) When heated, the motion of particles increases. The faster the particles move, the more they break away from each other. ○ Solids will melt into liquids. ○ Liquids evaporate into gases. When cooled, the motion of the particles will decrease. They get closer together. ○ Gases will condense into liquids. ○ Liquids will freeze into solids. 9 10 Phase Change Diagram 11 Atomic Structure 12  Atomic Structure All matter in the universe can be broken down into 118 different basic elements. The smallest units of these elements are called atoms. An atom is the smallest particle of an element that retains the element’s properties. Atoms are made up of three smaller (subatomic) particles called the proton, neutron, and electron. Each subatomic particle has its own charge. ○ Protons have a positive (+1) charge ○ Electrons have a negative (-1) charge ○ Neutrons have a no charge (0), or neutral 13 Atomic Structure Protons and neutrons are located in the center of the atom in an area called the nucleus. Electrons are located outside the nucleus, in areas called electron shells. The identity of an element is determined by the number of protons. Each element has a unique number of protons. For example, hydrogen has 1 proton and helium has 2 protons, and so on. The Atomic Number is the number of protons in an atom. 14  Electron Shells Electrons surround the positively charged nucleus in shells. The first shell can hold 2 electrons. The second shell can hold 8 electrons. The third shell can hold 18 electrons And so on… However the outermost shell of the atom can only hold 8 electrons. An atom with 8 electrons in the outer shell is considered stable. Hydrogen and helium atoms are an exception, since they so small they can only hold 2 electrons in their outer shell. 15 Covalent Bonds 16  Compounds and Seawater Water is a compound that consists of two atoms of hydrogen and one atom of oxygen. A compound is a substance that contains two or more different elements chemically bonded together. When Water molecule containing 2 hydrogen elements bond together to form compounds, they can have atoms and 1 oxygen atom very different properties than they do as individual elements. Seawater is a mixture. Mixtures contain a material made up of two or more different substances which are not chemically bonded. Elements and compounds in seawater include water, sodium chloride, carbon dioxide, glucose, and many more. 17 Composition of seawater 18  Why Do Atoms Bond Together? Most atoms can hold a maximum of 8 electrons in their outer shells, except for hydrogen and helium atoms which can only hold 2 electrons in their outer shells. Generally, atoms with 8 electrons in their outer shell are more stable and balanced. Atoms can interact with each other to stabilize their outer shells. Atoms may bond together by GAINING or LOSING electrons, or SHARING electrons in order to complete their outer shells. 19  Covalent Bonds In covalent bonds, atoms will share pairs of electrons with each other in order to complete their outer shell ○ 8 electrons needed for most atoms ○ 2 electrons for hydrogen Sharing electrons between two or more nonmetal atoms creates a covalent bond. Some atoms might share addition pairs of electrons, creating double or even triple bonds. 20  Water molecule Oxygen shares 4 electrons with two hydrogen atoms. Oxygen has a complete outer shell of 8 electrons Hydrogen atoms also complete shell of 2 electrons Water is a covalent molecule. 21  Reading Chemical Formulas Coefficient: large Covalent compounds can be number to the left of Element symbol: the molecule. represents the expressed as chemical formulas. Represents number elements in the of molecules They use element symbols, molecule coefficients, subscripts to identity the composition of the compound. 6H2 Subscript: small number to the O right of the symbol. Shows how many atoms in the molecule. No subscript means 1 atom. 22 Ways to represent a water molecule. 23  Covalent Bond Diagrams Covalent bonds be illustrated through dot and cross diagrams and line diagrams. Cl Cl Line diagrams show the structure of a covalent Dot and cross diagrams show the valence electron shells. compound. The line represents Electrons from one atom and shown as a dot and two shared electrons. electrons from another atom are shown as an X. Shared electrons are in the overlapping valence shells. 24 How many electrons do atoms have in their outermost (valence) shell? The columns of the main groups (1-8) indicate the number of valence electrons. Elements in group 1 have 1 valence electron Elements in group 2 have 2 valence electrons, and so on… 25 group number IUPAC group number example number of outer electrons number of covalent bonds 4 14 Carbon, C 4 4 5 15 Nitrogen, N 5 3 6 16 Oxygen, O 6 2 Chlorine, 7 17 7 1 Cl Using the periodic table to determine the number of covalent bonds. 26  How to diagram covalent bonds 1. Draw an overlapping circle around the symbol of each atom in the covalent bond, this represents outermost shell of electrons Diatomic nitrogen: N2 (valence shell). 2. Nitrogen is in group 5 (IUPAC 15) so it has 5 outer electrons and Each nitrogen atom has 5 needs 3 shared electrons to complete its outer shell. Draw the valence electrons (blue valence electrons of one atom as dots and the other as crosses. dots or green xs), 3 pairs Draw 3 pairs of shared electrons in the overlapping circle, this of electrons overlap so counts for both atoms. Please the remaining dots and crosses for each has 8 in total each atom. Two nitrogen atoms 3. Draw the line diagram by writing the symbol of the elements and lines ( ) representing two shared electrons (X⚫) N N bonded with 3 pairs of shared electrons 27  Carbon dioxide: CO2 Water: H2O O=O Oxygen: O2 Sulfur dioxide: SO2 Glucose: C6H12O6 Covalent Molecules. Lines represent pair of shared electrons. 28 Ionic Bonds 29  Ionic Bonds In ionic bonds, atoms will gain or lose electrons in order to have a full outer shell of 8 electrons (2 for hydrogen). Ionic bonds form when a metal atom gives up one or more electrons to a nonmetal atom. If an atom loses one or more electrons, it has an overall positive charge and becomes an positive ion (cation) If an atom gains one or more electrons, it has an overall negative charge and becomes an negative ion (anion) The positively charged and the negatively charged atom attract, forming an ionic bond 30 Sodium (Na) transfers an electron to Fluorine (F), creating an ionic bond. 31  Showing Ions in Chemical Formulas Ions are indicted by having a superscript at the top right of the formula (think exponent). This Sodium ion: Na1+ indicates the charge of the ion. Chlorine ion: Cl1- Sodium has a charge of 1+ so it lost one electron Calcium ion: Ca2+ Chlorine has a charge of 1- so it gained on electron Carbonate ion: CO32- Sometimes, covalent molecules like carbonate (CO3) can become ions. These are called polyatomic ions. 32  Sodium now has 1 Chlorine gained an more proton than it electron, so it is does electrons, negatively charged. giving it a charge of Sodium gives up an electron to +1 chlorine so both have a full outer shell. The positive sodium ion and negative chlorine ion Ionic bonding of sodium chloride attract and bond. 33 Crystal Lattices Many chloride and sodium ions can bond together, forming large crystal lattice structures. 34  Na+ Cl- Sodium Chloride: NaCl Calcium Carbonate: CaCO3 Salts are made from ionic bonds, which are very important compounds in our oceans. There are many types of salts found in the ocean, including: sodium chloride (NaCl) calcium carbonate (CaCO3) Magnesium sulfate: MgSO4 magnesium sulfate (MgSO4) 35 Hydrogen Bonds 36 Water Polarity Water molecules are polar. Polar molecules have a positive end and negative end due to an unequal sharing of electrons. In a water molecule, the hydrogen side is partially positive (𝛿+) and the oxygen side is is partially negative (𝛿-). Lower case delta (𝛿) is used to indicate the partial charge 37 Hydrogen Bonds Hydrogen bonds form between other water molecules. It is an intermolecular bond. This happens because the partially positive (𝛿+) hydrogen side of one water molecule is attracted to the partially negative (𝛿-) oxygen side of another molecule. 38 Properties of Water: Solvent Action Water is an excellent solvent due to its polarity. A solvent is a liquid that can dissolve a substance. Water is good at dissolving other polar substances, like sodium chloride for example. Water dissolves sodium chloride crystals ○ the partially negative oxygen side of water molecules pull the positive sodium ions apart ○ the partially positive hydrogen side pulls the negative chlorine ion apart 39  Properties of Water: Density As water freezes into a solid, molecules slow and hydrogen bonds space the molecules further apart than in liquid water. This forms a crystalline structure. The ice expands, meaning it takes up more space. This means that solid ice is less dense than liquid water, which is more space = less dense less space = more dense why it floats. 40 Iceberg floating in the Arctic ocean 41 Properties of Water: High Specific Heat Capacity Specific Heat Capacity is the amount of energy needed to raise a unit of mass of a substance by one degree Typically energy is measured in joules, mass is measured in grams, and temperature is measured celsius. Water has a high specific heat capacity, meaning it takes a lot of energy to change its temperature Because hydrogen bonds help hold water molecules together, more energy is needed break the hydrogen bonds in order to move the water molecules faster, thus increasing the temperature. 42