What is Chemistry? Learning goals 3 & 4

What is Chemistry? Chemistry is the science of matter and the changes it undergoes A large part of chemistry involves understanding the way chemicals react with each other. Living things require chemical reactions to survive Examples: Respiration, digestion, photosynthesis

Levels of Chemical Organization Atoms Nucleus—central core of atom In the nucleus there are… Protons—positively charged particles Neutrons—particles with NO charge Atomic number—number of protons in nucleus Atomic mass—number of protons and neutrons combined What makes up an atom’s atomic mass? The number of protons and neutrons combined.

Levels of Chemical Organization Atoms Energy levels—orbital regions around the nucleus that contain electrons Electrons—negatively charged particle Describe an energy level. Energy levels (shells) are the limiting regions in which orbitals are arranged.

Structure of an Atom Models of the atom. The nucleus—protons (+) and uncharged neutrons—is at the core. Electrons inhabit outer regions called energy levels (A), which look more like a cloud because the electrons do not stay in one place (B). This is a carbon atom, a fact that is determined by the number of its protons. All carbon atoms (and only carbon atoms) have six protons.(One proton in the nucleus is not visible in this illustration.)

Levels of Chemical Organization Element—a pure substance; made up of only one kind of atom Molecule—a group of atoms bound together in a group Compound—substances whose molecules have more than one kind of atom

Element, Molecule, or Compound Hydrogen H H2

Element, Molecule, or Compound H2O Na

How Many Elements and Atoms?? NaOH 3 NaCl 2 H2 2

Chemical Bonding Chemical bonds form to make atoms more stable Atoms react with one another in ways that make their outermost energy level full Atoms may share electrons or donate or borrow them to become stable What is a chemical bond? The energy that holds two atoms together.

Ionic Bonds Ionic bonds Ionic bonds form when positive and negative ions attract each other What is dissociation? Occurs when molecules dissolve in water because water molecules wedge between the ions and force them apart.

Ionic Bonds An Ion is an atom the has gained or lost electrons Positive ion—has lost electrons; as in Na+ or Ca++ Negative ion—has gained electrons; as in Cl– How is an ion formed? Ions form when an atom gains or loses an electron to become stable.

Ionic Bonds Ionic bonding. A, The sodium atom donates the single electron in its outer energy level to a chlorine atom having seven electrons in its outer level. Then both have eight electrons in their outer shells. Because the electron/proton ratio changes, the sodium atom becomes a positive sodium ion. The chlorine atom becomes a negative chloride ion. The positive-negative attraction between these oppositely charged ions is called an ionic bond. B, A cube-shaped crystal of sodium chloride (table salt).

Covalent Bonds A covalent bond forms when atoms share their outer electrons Covalent bonds do not easily break down in water Covalent bonding is used to form all of the major organic compounds found in the body What is covalent chemical bonding? Bonding that forms when atoms fill up their energy levels by sharing electrons rather than donating or receiving them.

Covalent Bonds Covalent bonding. Two hydrogen atoms move together, overlapping their energy levels. Although neither gains nor loses an electron, the atoms share the electrons, thereby forming a covalent bond.

Hydrogen Bonds Hydrogen bonds do not create new molecules Hydrogen bonds weakly bond to surrounding molecules Hydrogen bonds are present in 1) water 2)DNA 3)proteins