Electrons Atoms - the fundamental building blocks of all matter; basic unit of an element. Composed of 3 subatomic particles. - - - A particle outside the nucleus of an atom that has a negative electric charge. Atoms have the same number of electrons as protons. As a result, the negative and positive charges "cancel out." This makes atoms electrically neutral. For example, a carbon atom has six electrons that "cancel out" its six protons. Negative electrons are attracted to the positive nucleus. This force of attraction keeps electrons constantly moving around the nucleus. The region where an electron is most likely to be found is called an orbital. Electrons are located at fixed distances from the nucleus, called energy levels. Electrons at lower energy levels have less energy than electrons at higher energy levels Charge Subatomic Particles: - - Protons Neutrons Electrons - Particles may be electrically charged. Charge: is a property which defines the force that a particle will exert on other charged particles. Positive charges and negative charges will attract each other and come together. Two positive or two negative charges will push each other away. Nucleus - Also known as nucleons. Lies at the center of each atom. It contains nearly all of the atom's mass. The nucleus almost never changes under normal conditions, remaining constant throughout chemical reactions. Made up of pair proton and the neutron. Protons - A particle in the nucleus of an atom that has a positive electric charge. It is the number of protons that gives atoms of different elements their unique properties. NOTE: No two elements have atoms with the same number of protons. Neutrons - A particle in the nucleus of an atom that has no electric charge. Atoms of an element often have the same number of neutrons as protons. For example, most carbon atoms have six neutrons as well as six protons. What Makes Atoms Stick Together Valence Electrons - An electron that 'lives' in the last electron shell (or valence shell) of an atom. The atom will have one or more electron shells based on how many electrons the atom has. The number of valence electrons that an atom has tells us what it might be able to combined with to make something new. Chemical Bonding - A force that holds the atoms of various elements together in such compounds. It opens up the possibility of millions and millions of combinations of the elements, and the creation of millions and millions of new compounds. Everything that exists is made up of atoms held together in innumerable combinations that range from the: - G.N Lewis - - Developed the concept of valence electrons. He assumed that each noble gas atom had a completely filled outermost shell, which he regarded as a stable configuration because of the lack of reactivity. Since all noble gasses (except He) has 8 valence electrons, the observation came to be known as the octet rule. Octet Rule: In forming bonds, main group elements, gain, lose or share electrons to achieve the same electron configuration with 8 valence electrons. NOTE: The concept of valence electron is useful for understanding how atoms of different elements interact and why elements in the same group have similar properties. SIMPLEST MOLECULES: composed of only two atoms. COMPLEX MOLECULES: composed of thousands of atoms. Two Kinds of Chemical Bonds Link Atoms In Compounds 1. Ionic Bond - When atoms gain or lose electrons, they form positively or negatively charged atoms called ions. - An ionic bond forms when ions with opposite charges are attracted to each other. - Compounds held together by ionic bonds are ionic compounds. - Ionic bonds can break when ionic compounds are placed in water. - For example, NaCl, splits into sodium ions and chlorine ions when it is in water. - Ions are important in organisms. For example, your body uses sodium ions (Na+) and potassium ions (K+) to transmit nerve impulses. Calcium ions (Ca 2+) help muscles contract and relax. 2. Covalent Bond - A covalent bond forms when atoms shares electrons. - The shared electrons do not stay with one atom exclusively but pass between the atoms. - Compounds that are held together by covalent bonds are called covalent compounds. - Groups of two or more atoms that are held together by covalent bonds are molecules. - Carbon dioxide and water are examples of compounds that consist of molecules; they are called molecular compounds. - NOTE: Not all molecules are compounds. - Oxygen molecules (O2) consist of two atoms of oxygen held together by covalent bonds. Another example is nitrogen (N2). Variety of Organic Compounds: Functional Group - - The Chemistry of Carbon - Carbon can form many kinds of compounds because of the arrangement of its six electrons. Because carbon has four outer electrons to share, carbon atoms can form up to four covalent bonds with many kinds of atoms. Moreover, carbon atoms can form single, double or triple covalent bonds. Many organic compounds have special groups of reactive atoms that contain elements such as oxygen, nitrogen, sulfur or phosphorus. The special groups of atoms that carry out characteristic chemical reactions are called functional groups. Some important functional groups include: amine (-NH2), sulfate (-SO4), phosphate (PO4), carboxylic acid (-COOH) and hydroxyl or alcohol (-OH). They are involved in vital chemical reactions, while others are important to the chemistry of organisms. EXAMPLES: - PHOSPHATE GROUP: involve in the chemical reactions that form nucleic acids. AMINE GROUP: involve in the reactions that form proteins. CARBOXYLIC ACIDS: involved in the different reactions that form fats and proteins. Molecule Building - In all organisms, the different numbers and arrangements of carbon atoms produce an amazing variety of organic compounds. Some of the organic compounds contain only a few atoms, while others contain hundreds or thousands. Two Chemical Reaction Chemical Reaction: Process in which substances are changed into new substances by the breaking and forming of chemical bonds. 1. Dehydration Synthesis - Chemical reaction that forms covalent bonds between monomers. - The removal of water during the process of forming a compound. 2. Hydrolysis - The opposite reaction of dehydration synthesis; breaks polymers apart. - The word hydrolysis means “splitting by water”
