Lesson 1 Atoms and molecules.pptx

Atoms and Molecules Lesson : 1 Biol 101  OBJECTIVES Know the organization of life and the different types of elements Know about atom properties Know the different types of chemical bonds Define chemical reaction 2 ...

Atoms and Molecules Lesson : 1 Biol 101  OBJECTIVES Know the organization of life and the different types of elements Know about atom properties Know the different types of chemical bonds Define chemical reaction 2  Levels of Biological Organization The life is organized from the smallest atom composing matter to the largest Biosphere where the life exists. The cell is the barrier between biology and chemistry. Biol 101  The Elements of Life 92 natural elements 20-25% 75-80% Essential elements Some elements are toxic to Trace elements organisms As, Cr, Ni, Co… Required by organisms in Important for organisms to only minute quantities live a healthy life and reproduce O, C, H and N I (o.15mg/day) , Fe… Biol 101  Elements and Compounds Element is a substance that cannot be broken down to other substances by chemical reactions ex. Gold, carbon, oxygen… Compound is a substance consisting of two or more different elements combined in a fixed ratio ex. Table salt = sodium chloride (NaCl) = sodium (Na) + chlorine (Cl) 1:1 ratio Biol 101  Atoms and Subatomic Particles Atom is the smallest unit of matter having the properties of element The symbol of atom is the same symbol of element that is made up of this atom Atom is composed of smaller parts = 3 subatomic particles 1- Neutrons uncharged, exist in the nucleus of the atom 2- Protons positively charged, exist in the nucleus of the atoms 3- Electrons negatively charged, exist around the nucleus Biol 101  Atomic Number / Mass Number Atomic number = Number of protons All atoms of an element have the same number of protons in their nuclei Atomic number= number of protons = number of electrons Mass number = Atomic Mass = Number of protons + Number of neutrons Hydrogen is the simplest atom which consist of 1 proton & 1 electron Mass of an electron = 1 / 2000 that of a neutron or proton we can ignore electrons when computing the total mass of an atom Biol 101  Isotopes In nature, an Element exists as a mixture of its isotopes. They are different atomic forms of the same element They have the same number of Protons. They have different number of Neutrons Isotopes behave identically in chemical reactions. Some of them are stable and others are radioactive Biol 101  Radioactive Isotopes Radioactive isotope is one in which the nucleus decays spontaneously giving off particles and energy Radiation can damage cellular molecules depending on the type and amount of radiation absorbed by the organism. Radioactive Isotopes are readily detected so they are useful in: - dating relics of past life (fossils) - Tracers to follow atoms through metabolism - Diagnostic tool in medicine Biol 101  Electrons and Energy Levels The Electrons in an atom vary in the amount of potential energy they possess depending on the distance separating them from the nucleus. Electrons that are more distant from the nucleus, have greater Potential Energy. Electrons can move from shell to shell: - If it moves from higher to lower level, it will Release/Lose energy as heat. - If it moves from lower level to higher level, it will Achieve/Absorb energy. Biol 101  Electrons and Orbitals The Electron is found 90% of the time in orbitals (three dimensional space around the atom’s nucleus) An orbital can be occupied by only 2 electrons The 1st shell has only one s orbital (1 s) The 2nd shell has 4 orbitals (one s orbital and three p orbitals (2s, 2p) so it can be occupied by 8 electrons. The 3rd and other higher shells also have s and p orbitals as well as other orbitals Biol 101  Electrons and Chemical Properties During chemical reactions, atoms approach each other and interact through the involvement of electrons only. Valence Shell is the Outermost/Last shell that fills of Electrons. Valence Electrons is the number of Electrons that are in the Valence Shell. Valence Shell and Valence Electrons play an important role in: Chemical interactions\ reactions, bonding, and Stability of atoms: -Atom with a completed Valence Shell is Unreactive/ inert/ stable: will not interact with other atoms. (ex. Helium, Neon, Argon) -Atom with incomplete valence shell is chemically reactive Biol 101 1) Find the Valence shell and Valence electrons of each atom 2) Deduce if each atom is stable or unstable. 3) What do atoms existing in the same row (period) have in common? 4) What do atoms existing in the same column have in common? Biol 101  Chemical Bonding Atoms with incomplete Valence Shell can share or transfer Valence electrons with other atoms to complete their valence shell. There are 2 types of chemical bonds: Strong and Weak: Strong bonds aim to make molecules. It has 2 types: Covalent bond and Ionic bond Weak bonds aim to link between molecules. It has 2 types: Hydrogen bond and Van Der Waals interactions Biol 101  Covalent Bond Covalent bond is a strong bond It is the sharing of valence electrons by 2 atoms forming molecule. If the 2 atoms have the same electronegativity, so they attract electrons equally making Non-polar covalent bond. Example: Methane (CH4) If the 2 atoms have different electronegativity, the shared electrons are more attracted by the more electronegative atom making Polar covalent bond. Example: Water (H2O) Biol 101 Electronegativity: is the ability of an Atom to attract electrons in a chemical bond. Biol 101  Ionic Bond Ionic bond is a strong bond It is the attraction between 2 oppositely charged atoms (ions). If the Atom gains an Electrons, it will turns to an ion with a (-) charge (anion) If the Atom loses an Electrons, it will Sodium (Na): donates/ loses its Valence Electron. turns to an ion with a (+) charge Chlorine (Cl): gains a new electron to its Valence Shell (cation) Biol 101  Weak Bonds 1- Hydrogen Bond is an attraction between a hydrogen atom of a molecule and a more electronegative atom of other molecule 2- Van der Waals Interaction is an attraction between positive and negative regions of nearby molecules. Biol 101  Chemical Reaction Chemical reactions change reactants into products while conserving matter All chemical reactions are theoretically reversible Biol 101 Biol 101