Chemistry for A&P students. Why should I care about chemistry?

Transcription

1 Chemistry for A&P students Why should I care about chemistry? A. As humans we are made up of atoms, many are bound to each other to form molecules (also called chemicals). Every anatomical structure in our body is made up of thousands of atoms intricately and specifically connected to each another. The functioning, or physiology, of our body depends on how atoms and molecules associate and react with each other. So a basic understanding of chemistry is necessary if we are to fully grasp Anatomy and Physiology. B. Normal physiology (everyday body functions) For example: Blood: Red blood cells contain the molecule hemoglobin. Iron in the hemoglobin binds to oxygen and facilitates the movement of oxygen from the lungs to the rest of the body. C. Allied Health i. Nutrition: What is food? A butt load of molecules like glucose, fats, carbohydrates. Why do we eat? For energy and building blocks for components of the body. ii. Nursing: Patient care includes understanding blood chemistry and interpreting blood test measurements, monitoring variables such as ph and blood pressure, delivering IV solutions, injections and drugs. iii. Dentistry: Fluoride is important for strong teeth and bones. Sugar: increases dental decay, why? Feeds anaerobic bacteria that live in our mouths, the lactic acid waste produced is what causes the tooth decay. i. Respiratory Care: Breathing: inhale: oxygen, exhale: carbon dioxide. Monitor devices that provide oxygen or medicine in the form of a mist or gas to patients. iv. Radiology technology: Use radiation and radioisotopes to both treat and detect cancer. Imaging techniques include x rays, CT and MRI scans.

2 The Atom: is the smallest intact component of all matter, Atoms are tiny: Macroscale Microscale Nanoscale Atomic scale Figure 1 Matter at different scales Mag. Mag. Mag. X1000 x1000 X1000 x1000 X10 Drop of blood Red blood cells Hemoglobin molecule Single atom There 111 different types of atoms which make up the elements. An element is composed of 1 type of atom: it cannot be broken down to a simpler form. Oxygen is an element composed of only oxygen atoms Iron is an element composed of only iron atoms. A chemical compound is composed of 2 or more atoms held together by bonds. E.g. Water 2 hydrogens and 1 oxygen. Fig. 2 Anatomy of the atom ELECTRON PROTON NEUTRON

3 Subatomic particle Charge Mass Location within Atom Proton +1 1 amu Nucleus Neutron 0 1 amu Nucleus Electron amu Orbitals 1amu=1.66x10-24 g Since electrons practically have no mass, the mass of an atom comes from its protons and neutrons. Complete EXERCISE 1(see accompanying worksheet) Atomic number: # of protons. Carbon has 6 protons, atomic # = 6 Oxygen has 8 protons, atomic # = 8 Iron has 26 protons. Mass number: # protons + # neutrons Carbon has 6 protons and 6 neutrons, Atomic mass = 12 Element symbol: every element has been assigned a 1 or 2 letter element symbol. Carbon (C), Oxygen (O), Iron (Fe) The Period Table Each box in the periodic table lists the atomic number, element symbol and atomic mass. 6 C Atomic number Element symbol Atomic mass The elements are listed in order of atomic number. Every element has physical and chemical properties that can be observed. Physical property: color, density, boiling point (Temp at which it changes from liquid to gas) Chemical properties: refer to its behavior in the presence of other elements. The element may undergo a chemical change when it combines with other elements or molecules to form a new compound. This process is called a chemical reaction. E.g. Iron undergoes a chemical change in

4 the presence of oxygen to form a new compound, Iron oxide. The iron reacts with oxygen to form compound in which the iron is bound to the oxygen. The table has 7 rows (periods) and 18 columns (groups), elements are ordered such that elements in the same groups have similar physical and chemical properties. Example: Group1A (alkali metals), Group 7A (halogens) Complete EXERCISE 2(see accompanying worksheet) Metals and Nonmetals Blue: metals Orange: non metals Have very different physical and chemical properties, compare Gold or silver in jewelry (shiny, malleable) to Graphite in your pencil (Carbon, dull, brittle) Elements important in the body: Building blocks: C,H,N,O,P and S (make up the chemical structure of most molecules in the body). Macronutrients: Na, K,Mg,Ca,P,S,Cl Micronutrients:V,Cr,Mn,Co,Cu,Zn,Mo,Si,Se,Fe,I Macro and micro nutrients play a critical role in bodily functions. Complete EXERCISE 3(see accompanying worksheet) Electrons The main factor determining physical and chemical characteristics are the electrons in the outermost orbit or shell of an atom. These are called valence electrons. Electrons orbit the nucleus in layers (like an onion), there are inner core electrons and outer valence electrons. Electron shells are designated a number (n), the lower the value of n, the closer the electrons are to the nucleus: Electron shell 3 (n=3) Electron shell 2 (n=2) Electron shell 1 (n=1)

5 The electrons in the outermost shell are the valence electrons. The different shells have different energies associated with them. n=1 has is the 1st energy shell, n=2 is the 2 nd energy level etc. A given shell, n, can accommodate 2n 2 electrons. Electron shell, n Maximum number of electrons, 2n In the most stable form of an atom, the electrons will occupy the lowest shell levels, until the maximum number of electrons allowed in a shell has been reached: Period Element Atomic number n=1 n=2 n=3 1 Hydrogen 1 1 Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Florine Neon Sodium Magnesium Aluminium Shaded boxes indicate valence electrons. Elements within the same groups (columns on the periodic table) have the same number of valence electrons. E.g. Hydrogen, lithium, sodium and potassium (group 1A) all have 1 valence electron. They differ in the shell that contains the valence electron. Hydrogen has its valence electron in the n=1 shell, lithium has its in the n=2 shell, etc. Complete EXERCISE 4 (see accompanying worksheet)

6 Compounds (molecules) -substances composed of 2 or more atoms. -in nature, most atoms bond to each other to form compounds -there are 2 basic types of compounds: a. ionic compounds b. covalent compounds -the 2 differ in the how the atoms are held together: the chemical bonds Ionic Compounds -Formed when a metal atom transfers some or all of its valence electrons to a nonmetal, creating charged units called ions. Like charges repel and opposites attract. A positive and negative charged ion are attracted to each other, this is called electrostatic attraction. -The electrostatic attraction between oppositely charged ions is the glue that holds ions together in an ionic compound. Ionic compounds are also called salts. Ion: an atom that has lost or gained one or more valence electrons, so it has an unequal number of electrons and protons, and this gives the ion either a positive (+) or negative (-) charge. The magnitude of the charge on an ion is equal to the difference between the number of protons and electrons. For example: Sodium (Na), atomic number: 11. Elemental Na has 11 protons and 11 electrons. Na tends to lose its 1 valence electron. This leaves Na with 11 (+) protons and 10 (-) electrons So Na ions have a net +1 charge This is written: Na + Chlorine (Cl), atomic number:17 Elemental Cl has 17 protons and 17 electrons. Cl tends to gain an electron This leaves Cl with 17 (+) protons and 18 (-) electrons So Cl ions have a net -1 charge Written as Cl -

7 Negatively charged ions like Cl - are called anions Positively charged ions like Na + are called cations Ions are formed from the gain or lose of electrons. The number of protons never changes. Metals tend to lose electrons, Nonmetals tend to gain electrons. Why do metals tend to lose electrons? By losing all of its valence electrons, an element is left with its outermost shell full. This arrangement is very stable. (From Fig. 2-3 Brewer, 2010) Group 1A tend to lose 1 electron, Group 2A tend to lose 2 electrons Transition metals: more complicated and are not as easily predicted, Iron can form Fe 2+ or Fe 3+ Non-metals in groups 5A, 6A and 7A tend to gain electrons to form anions. Group 7A: halogens all form anions with a -1 charge. Group 6A form anions with a -2 charge. F F - (From Fig. 2-6 Brewer, 2010)

8 Some common ionic forms of some important ions can be found in Fig. 2-5 (Brewer, 2010) Group 4A: Unique group. These elements have a half full valence shell. They do not gain or lose electrons. Carbon is the most important one: it shares electrons with other atoms, which how covalent bonds are formed. Complete EXERCISE 5 (see accompanying worksheet) The Ionic Lattice Anions and cations attract each via electrostatic attraction to form an ionic compound. For example sodium chloride, NaCl, (table salt). These electrostatic attractions are called ionic bonds. Electrolytes When placed in water the ionic lattice falls apart, the ions separate and become surrounded by water molecules. The salt is said to be dissolved in water. Ions dissolved in water are called electrolytes. Cells are composed of mostly of water and contain many electrolytes that are critical to its function. The most important electrolytes are Na +, K +, Ca 2+, Mg 2+ and Cl -. For example: Na + and K + transmit electrical signals in nerve cells. Covalent compounds Most compounds (molecules) are formed via covalent bonds between nonmetal atoms: proteins, carbohydrates, lipids, DNA, hormones etc. A covalent bond is formed when 2 nonmetal atoms come together and share some or all of their valence electrons. By sharing, nonmetals can achieve a full outer shell of 8 electrons, or in the case of hydrogen, 2 electrons. A covalent molecule has a unique composition that is described by its molecular formula. In a molecular formula each atom is listed in alphabetical order, followed by a subscript indicating how many of that type of atom are in the molecule. For example: water H 2 O The covalent bond Single bonds: Each atom shares one of its valence electrons with the other atom. For example: H 2 For example CH 4

9 E.g. Methane CH 4. The carbon atom shares each of its 4 valence electrons with a single hydrogen atom, each hydrogen atom shares its valence electron with the carbon atom: The diagram shows how to draw the covalent bonds of a methane molecule. The left image shows the Lewis dot structure. This serves as an electron booking tool. When the atoms share 2 electrons, 2 dots are placed between the 2 atoms to indicate that both atoms share the electrons. On the right, shared electrons are represented by a line. Double and triple bonds: Atoms are not limited to sharing 2 electrons. They can share 4 electrons (C 2 H 4 ) to form a double bond or 6 electrons to form a triple bond (C 2 H 2 ). You can predict the structure of a molecule by arranging electrons so that each atom has a full outermost shell, known as the Octet Rule. Molecules such as C, N and O all need 8 electrons to fill their outer shell. Hydrogen needs 2. (A detailed description of Lewis dot structures can be found in (Brewer, 2010)) Complete EXERCISE 6 (see accompanying worksheet) REFERENCE: Essentials of General, Organic and Biochemistry. Guinn D, Brewer R ISBN: