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Principles of Chemistry

Principles of Chemistry Slide 1 – Introduction In unit 2 we will have an overview of basic chemistry, then move on to a study of organic molecules. Then we will discuss the digestive system. Let’s begin our study of chemistry. Slide 2 – The Atom The smallest unit of matter is the atom. An atom consists of protons, neutrons, and electrons. Protons are positively charged. The proton is in the nucleus of an atom. A proton has a mass of one atomic unit. Another subatomic particle that is found in the nucleus is the neutron. Like the proton, neutrons have a mass of one atomic unit, however neutrons DO NOT have a charge. A third subatomic particle is the electron. Electrons are found outside of the nucleus and are often depicted as circling the nucleus just as the earth revolves the sun. Electrons are negatively charged and weigh almost nothing. Slide 3 – Elements The number of protons is different for each type of atom. An element consists of only one type of atom. The number of protons for each element is known as the atomic number for that element. Looking at atoms of hydrogen, carbon, nitrogen, and oxygen, we can see that hydrogen’s atomic number is one, which is the number of protons in its nucleus. An atom that has 6 protons is carbon. If the atom had 7 protons, it wouldn’t be carbon, but nitrogen. Each element is also abbreviated to a one, two, or in rare instances a three letter abbreviation. For example, nitrogen is abbreviated N and oxygen abbreviated O. Slide 4 – Atomic Structure Atoms typically have the same number of protons as electrons. This means that an atom usually has no charge; however atoms have the ability to gain or loose electrons, but not protons. Therefore an atom can have a positive or negative charge; this is known as an ion. The electrons are arranged around the nucleus in a specific order, which we will discuss shortly. Slide 5 – Atomic Mass As discussed earlier protons and neutrons have mass. Each of these particles weighs one atomic unit. By adding the number of protons to the number of neutrons in an atom, we can calculate the atomic mass of an atom. Since the atomic number is also the same as the number of protons in an atom, you can also calculate the number of neutrons in an atom by subtracting the atomic number from the atomic mass. Slide 6 – Isotopes We have said that the number of protons defines an element. However an element can have varying amounts of neutrons. For examples some elements of carbon have 6 neutrons, others have 7 neutrons, and still others have 8 neutrons. Elements with different numbers of neutrons are called isotopes. Isotopes of an element are distinguished by their mass. Using carbon as an example, elements of carbon with 6 neutrons have a mass of 12 and are called carbon 12. Elements of carbon with 7 neutrons have a mass of 13 and are called carbon 13. Elements of carbon with 8 neutrons have a mass of 14 and are called carbon 14.
Principles of Chemistry Slide 7 – Isotopes YouTube video – Tennis ball isotopes: The Concept of Isotopes Slide 8 – Radioactivity and Half life As stated previously, isotopes are atoms of the same element that have a different number of neutrons. In other words, the atoms have the same number of protons but a different number of neutrons in the nucleus. Because the like charges of the protons repel each other, there are always forces trying to push the atom nucleus apart. The nucleus is held together by something called the binding energy. In most cases, elements like to have an equal number of protons and neutrons because this makes them the most stable. Stable atoms have a binding energy that is strong enough to hold the protons and neutrons together. Even if an atom has an additional neutron or two it may remain stable. However, an additional neutron or two may upset the binding energy and cause the atom to become unstable. Radioactive decay is the spontaneous breakdown of an atomic nucleus of an unstable atom resulting in the release of energy and matter from the nucleus. Not all of the atoms of a radioisotope decay at the same time, but they decay at a rate that is characteristic to the isotope. The rate of decay is a fixed rate called a half-life. The half-life of a radioisotope describes how long it takes for half of the atoms in a given mass to decay. Some isotopes decay very rapidly and, therefore, have a high specific activity. Others decay at a much slower rate. Slide 9 – Carbon Dating YouTube video – Carbon Dating Slide 10 – Check Your Understanding Now that we have learned about radioactivity and half-life, let’s check your knowledge of the subject. The following slides will have a series of questions on the topic. Be sure to click “Submit” after answering each question. Slides 11 through 13 – Radioactivity and Half-life Interactive Quiz A non-graded assessment to test your understanding of radioactivity and half-life. Slide 14 – Periodic tables Elements are defined by their atomic number, represented by a short abbreviation, and positioned on the periodic table of elements based on their properties. As we shall see, the properties of elements are based on their electrons. Although periodic tables may differ from each other slightly, they each contain an atom’s atomic number, symbol and mass. The atomic mass often is a number with decimal figures because it is an average of all of the isotopes for that element. Slide 15 – Elements important to biology In biology some elements are more important for you to know. In living organism organic molecules, those consisting of carbon and hydrogen are prevalent, however other elements are important. You should recognize the elements oxygen, phosphorus, nitrogen, potassium, calcium, chlorine, magnesium, sodium, and iron.
Principles of Chemistry Slide 16 – Electron Orbitals Earlier we mentioned that electrons are outside of the nucleus and give each element its properties. Electrons are arranged around the nucleus in a specific order. These arrangements are called orbitals. Electrons can move between these levels and gain or release energy as they do so. The first orbital, closest to the nucleus, can hold a maximum of two electrons. The second orbital can hold a maximum of eight electrons. The third orbital can hold a maximum of 18 electrons, and the fourth orbital can hold a maximum of 32 electrons. There are more levels, but they are beyond the scope of this course. Slide 17 – The Octet Rule The octet rule states that atoms are stable when they have 8 electrons in their outer shell. Atoms fulfill the octet rule by gaining, losing, or sharing electrons. This is why atoms bind with one another to satisfy the octet rule. Slide 18 – Carbon example Let’s look at carbon. Carbon has an atomic number of 6, so therefore it has 6 protons and six electrons. The electrons are distributed around the shells from the inside out. The first two electrons are in the first orbital and the remaining 4 electrons are in the second orbital. In order to satisfy the octet rule carbon need to bond with other atoms so that it has 8 electrons in its outer shell. Slide 19 – Check Your Understanding Now that we have learned about atomic structure, let’s check your knowledge of the subject. The following slides will have a series of questions on the topic. Be sure to click “Submit” after answering each question. Slides 20 through 25 – Atomic Structure Interactive Quiz A non-graded assessment to test your understanding of atomic structure. Slide 26 – Types of Bonds There are two basic types of bonds, one type is where electrons are gained or lost between atoms, and the other type is where electrons are shared between atoms. Ionic bonds are the bonds that occur when electrons are gained or lost from atoms. When electrons are shared, these bonds are called covalent bonds. Within covalent bonding sometimes the electrons are shared evenly, these are called non-polar covalent bonds. At other times during covalent bonding, the electrons are shared unevenly; this is called polar covalent bonding. Slide 27 – Example of Ionic bonding First let’s look at an ionic bond. In this reaction sodium will combine with chlorine to form sodium chloride, or table salt. Sodium has an atomic number of 11. Looking at sodium we can see that it has two electrons in its first shell, 8 electrons in the second level, and one electron in its third outer shell. It would be easier for sodium to give away the electron in its last shell instead of trying to gain another 7 electrons. When sodium does this, it becomes positively charged because it now has more protons than electrons. Sodium is now an ion.
Principles of Chemistry Slide 28 – Ionic bonding Chlorine has an atomic number of 17. This means that Chlorine has two electrons in its first shell, 8 electrons in its second shell, and seven electrons in its outer shell. It would be easier for chlorine to gain one electron instead losing seven electrons. When this happens, a chloride ion is formed that is negatively charged because the atom now has more electrons than protons. Slide 29 – Ionic bonding What is an ionic bond? When sodium donates the sole electron in its outer shell to chlorine each has satisfied the octet rule. Sodium now has a full outer shell with 8 electrons and chlorine has 8 electrons in its outer shell. Each is also a charged ion and opposites attract. The positive charge of sodium is attracted the negative charge of chlorine to form an ionic bond. Slide 30 – pH scale Sometimes hydrogen gives its lone electron up and forms a hydronium ion. Substances that contain a lot of hydrogen ions are called acids. Substances that have few hydrogen ions, but have a lot of another ion, hydroxide, are called bases. We use the pH scale to determine if a substance in an acid or a base. A substance with a pH below 7 is an acid. A substance with a pH above 7 is a base. A pH of 7 is considered neutral. Look at the pH scale on this slide. Most of your body fluids, with the exception of stomach acid have a pH around 7. Anything added to your body that is too acidic or too basic will harm you. For example if you pour acid on your skin, it will burn. Now you have a better understanding as to why acid rain causes damage to trees and other organisms. Just like you, these organisms were designed to exist in a neutral pH. Anything too acidic would damage them just as it would you. Slide 31 – Check Your Understanding Now that we have learned about acids and bases, let’s check your knowledge of the subject. The following slides will have a series of questions on the topic. Be sure to click “Submit” after answering each question. Slides 32 through 35 – Acids and Bases Interactive Quiz A non-graded assessment to test your understanding of acids and bases. Slide 36 – Covalent bonding Now let’s turn our attention to the covalent bond. In a covalent bond electrons are shared. They can be shared even or unevenly. We will first look at a polar covalent bond where electrons are not shared evenly between the atoms. An example of a polar covalent bond is the bond between hydrogen and oxygen in a molecule of water. Water is composed of two hydrogen atoms and one oxygen atom and its chemical formula is H2O. Slide 37 – Hydrogen Hydrogen is the smallest of all the elements. It has an atomic number of one; therefore hydrogen has only one proton and one electron. The one electron is found in the first energy level. Remember that the first level can only hold two electrons. Hydrogen will have to find one more electron to fill up this energy level to be stable. This is the exception to the octet rule.
Principles of Chemistry Slide 38 – Oxygen Oxygen has an atomic number of 8; it has 8 protons and 8 electrons. Two of these electrons will go into the first level and the remaining six will go into the second level. Oxygen wants two more electrons to fill up the second level and satisfy the octet rule. Slide 39 – Water is a polar molecule Oxygen is not quite strong enough to take the electrons from hydrogen, so it is forced to share and form a covalent bond. Oxygen is strong enough to keep the electrons most of the time. This causes oxygen to have a partial negative charge. With regards to the two hydrogen atoms in water, since they do not have the electrons most of the time, they have a partial positive charge. This situation creates a polar covalent bond. Slide 40 – Hydrogen bonds The polar covalent bonds in water give it many of the important properties that make it necessary for life. The partial negatively charged atoms of oxygen will be attracted to the partial positively charged atoms of hydrogen, creating a unique structure for water. The attraction between the oxygen and hydrogen form hydrogen bonds. Slide 41 – Why does salt dissolve in water? The fact that water has slight charges, means that only certain substance can dissolve in water. Let’s go back to salt. It was made of positive sodium ions and negative chloride ions. In water salt breaks apart into its ions, with the positive sodium being attracted to the negative oxygen and the negative chlorine being attracted to the positive hydrogen. Other polar compounds will also dissolve in water because of the attraction of the opposite charges. Substances that are not polar covalent or ionic compounds will not dissolve in water. Things that dissolve in water are called hydrophilic compounds, and those that do not dissolve in water are called hydrophobic compounds. Slide 42 – Methane is a non-polar compound Now let’s look at an example of a non-polar covalent bond. Carbon forms a bond with four hydrogen atoms to form the compound methane. As we said before, carbon needs four electrons to complete its outer shell, while hydrogen just needs one electron. Four hydrogen atoms will share their electrons with carbon to fill each of the atoms outer shells. Carbon is not as strong as oxygen, so its shares the electrons somewhat evenly with the hydrogen atoms. Because methane is formed by non-polar covalent bonds, it would not dissolve in water. Slide 43 – Movement in and out of Cells Now that we have talk about some of the chemistry of biology, let’s discuss one application of it. Cells, which are the smallest unit of life, are surrounded by a structure called the cell membrane. The function of the cell membrane is to control the passage of materials in and out of the cell. Because the cell membrane is selective about which material can pass through it, cell membranes are semi- or selectively permeable. Some of the molecules that we have discussed that can easily pass through the cell membrane are oxygen, carbon dioxide, and water.
Principles of Chemistry Slide 44 – Diffusion One way that materials enter and exit cells is through the process of diffusion. Diffusion is the movement of substances from an area of high concentration to an area of low concentration. Because of the concentration gradient, this type of movement across a cell membrane does not require the input of energy, it is called passive transport. Some examples of diffusion include: the movement of oxygen from your lungs into your blood; the movement of carbon dioxide from your blood into your lungs; and the spraying of a room deodorizer. Slide 45 – Osmosis Another form of passive transport is osmosis. Osmosis is the diffusion of water. This means that across a cell membrane, water will move from an area of high concentration to an area of low concentration. Osmosis is the reason you can not drinking sea water if you are stranded on a deserted island. The concentration of water is greater in your cells compared to the sea water outside of your cells. By the process of osmosis, water will move out of your cells, causing your cells to shrink and die. Cells could burst if they are exposed to pure water, since the concentration of water is greater on the outside of the cell. Water would then move into the cell. Slide 46 – Passive Transport YouTube video – Passive Transport Slide 47 – Check Your Understanding Now that we have learned about diffusion and osmosis, let’s check your knowledge of the subject. The following slides will have a series of questions on the topic. Be sure to click “Submit” after answering each question. Slides 48 through 53 – Diffusion and Osmosis Interactive Quiz A non-graded assessment to test your understanding of diffusion and osmosis. Slide 54 – Summary This slide is a summary of all of the “Check Your Understanding” questions from this lecture. Be sure to review the questions you answered incorrectly. Slide 55 – Active Transport Active transport is another method that cells use to move materials across the cell membrane. In active transport, there is a use of energy to move materials against the concentration gradient. This means that energy is used to move materials from an area of low concentration to an area of high concentration. The energy that is used is an organic molecule called ATP. There are three criteria need to define active transport. These are that materials are moved: 1. through a membrane 2. uses a protein carrier 3. uses ATP
Principles of Chemistry Some examples of active transport include: Movement of glucose into cells from the blood Sodium potassium pump Absorption of minerals Slide 55 – Active Transport YouTube video – Active Transport

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