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Home , Chemical compound

CH 2- THE OF LIFE

. The study of chemistry begins with the basic unit of , the . . The Greek philosopher Democritus called the smallest fragment of matter the atom, from the Greek word atomos.

Atoms (cont.)

. Placed side by side, 100 million atoms would make a row only about 1 centimeter long. . Atoms contain subatomic particles that are even smaller. Atoms (cont.)

. What three subatomic particles make up atoms? Atoms (cont.)

. The subatomic particles that make up atoms are . . neutrons . Atoms (cont.)

. Smallest property of an element that still has the properties of that element . “The building blocks of matter” . Atoms are made of smaller (subatomic) particles arranged in a particular way . p+ () . n° (neutron) . e- () Atoms (cont.)

. Protons and neutrons have about the same . . Protons are positively charged particles (+). . Neutrons carry no charge (◦). . Strong forces bind protons and neutrons together to form the nucleus, which is at the center of the atom. Atoms (cont.)

. The electron is a negatively charged particle (−) with 1/1840 the mass of a proton. . Electrons are in constant motion in the space surrounding the nucleus (e- cloud). Atoms (cont.)

. The subatomic particles in a atom. Atoms (cont.)

• Electrons are attracted to the positively charged nucleus but remain outside the nucleus because of the energy of their motion. • Because atoms have equal numbers of electrons and protons, and because these subatomic particles have equal but opposite charges, atoms are neutral.

Atoms (cont.)

. Atomic number- # of p+ AND electrons in an atom . Mass number- total # of p+ + n° in an atom . # of neutrons- mass number- atomic number . - charged atom (can gain or lose electrons) . If an atom gains e-, does it have a positive or negative charge? . What if the opposite is true? . LEP-GEN (Lose Electrons Positive, Gain Electrons Negative) . Where can the characteristics of all atoms be found?

Practice

. Atomic #? . Atomic mass? . # of neutrons? More Practice

. Atomic #? . Atomic mass? . # of neutrons? Elements

. Substances that can’t be broken down into simpler substances . Pure substance made of only ONE type of ATOM . Represented by one or two letter symbol (Ex. C, H, O, Al, Fe, He, Ga, Pt, Au) . Noble . Elements that can exist alone (don’t combine with other atoms…usually!) . Ex. He, Ne, Ar . Mike Stanfill, Private Hand - Flash Animation - The Elements, by Tom Lehrer Elements (cont.)

. . Reaction of Sodium with .

Elements (cont.)

• More than 100 elements are known, but only about two dozen are commonly found in living .

. Atoms of the same element that have different #’s of n° . Ex. C-14 and C-12 . Both have 6 p+ . C-14 (8 n°), C-12 (6 n°) (cont.)

. Isotopes are identified by their mass numbers. . For example, has three isotopes—carbon-12, carbon-13, and carbon-14. Each isotope has a different number of neutrons. Isotopes (cont.)

. Q- How are all of the isotopes of an element similar? Isotopes (cont.)

. A- Because they have the same number of protons and electrons, all isotopes of an element have the same chemical properties. Isotopes (cont.) Isotopes of Carbon

6 electrons 6 protons 768 neutrons Isotopes (cont.)

. Radioactive Isotopes . Some isotopes are radioactive, meaning that their nuclei are unstable and break down at a constant rate over time. . Although the radiation these isotopes give off can be dangerous, they have important scientific and practical uses. Isotopes (cont.)

• Radioactive isotopes can be used: . to determine the ages of rocks and fossils. . to treat cancer. . to kill bacteria that cause food to spoil. . as labels or “tracers” to follow the movement of substances within an . Chemical Compounds

. Chemical Compounds . In nature, most elements are found combined with other elements in compounds. . A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions. . The physical and chemical properties of a compound are different from the elements from which it is formed. Chemical Compounds

• Scientists show the composition of compounds by a kind of shorthand known as a molecular .

• Water, H2O, contains two atoms of for each atom of . • The formula for table , NaCl, indicates that sodium and chlorine combine in a 1 : 1 ratio. Molecular

. Shows numbers of and atoms . Molecules = coefficient (the number in front) of molecular formula (ex. 3H2O = 3) . Atoms = # of atoms in compound

(ex. H2O = 2 , 1 Oxygen = total of 3 atoms in this compound) . Total # of atoms = (Coefficient) x (# of atoms) . How many molecules and atoms do each of the following have?

. 3 H2O . 2 C6H12O6 . 4 NaCl

. CO2

Structural formulas

. Shows how the atoms are connected in a compound. Each element requires 1-4 lines to connect it to other atoms (see )

. Ex. C2OH6 . Is there a problem in drawing this? H H H H | | | | H - C - C - O - H H - C - O - C - H | | | | H H H H

. Have same molecular formula but different structural formulas

. C3H8O

Energy shells

. Located in the e- cloud . 1st shell holds a maximum of 2 e- . All other shells hold up to 8 e- Electron Configuration

. Drawing of how many e- are in each orbital. . Must know atomic number so know how many protons (and therefore how many electrons) an element has . Ex. O has atomic # of 8 therefore has 8 e- . Electron configuration = 2) 6) . Ex. Al has atomic number of 13 . Electron configuration = 2) 8) 3)

. Shows how elements bond together by sharing e- . Several steps involved in determining valence . What is an e- orbital? . How many e- can fit in each orbital? . What do we have to know before we can determine valence? Valence electrons

. Number of e- in the outermost energy shell - . Ex. O2 has ______valence e Valence (cont.)

. Where are the valence e- located? . Answer: In the LAST orbital!!! . ______+7 2) 5) . ______+5 2) 3) . Each orbital wants to be FULL to be happy!! . To determine valence, always take the path of least resistance (always choose the lowest number to gain or lose to make the orbital full)

Valence (cont.)

. If an atom loses e-, does it become more positive or more negative? . This positive or negative will always be the sign in front of the valence . The valence number is found by figuring out how many e- must be lost or gained to make the atom happy (have the last orbital full!) Valence (cont.)

. In summary, to find valence: 1. Look up the atomic number (# of p+) 2. Determine the electron configuration 3. Determine the # of valence e- (# of electrons in last shell) 4. Determine if it is + or – valence (if it gains e- it becomes more negative and vice versa) 5. Determine valence by how many e- it would have to lose or gain to be happy Valence (cont.)

. Want an easier way to find valence? . Label your periodic table!

Chemical bonds

. Forces that hold atoms together . Can be single, double, or triple bond . Depends on how many pairs of electrons are shared between elements . Single bond . Double bond . Triple bond

Bond Lines

. All elements have the ability to bond with other element(s) . Can have anywhere between 1 and 4 bond lines . How do we know how many bond lines each element has? . Answer: the number of bond lines is the same of the valence of the element (without the + or – sign) Bonding (cont.)

. Ex. Cl has a valence of -1, so it has one bond line. . Ex. C has a valence of ±4, so it has four bond lines. . Ex. N has a valence of -3, so it has three bond lines. Bonding rules

. Each element must have the correct # of bond lines attached to it . # of bond lines is determined by ______?

. Ex. O2 has valence of -2, so it has ______bond lines. . Ex. C has a valence of ± 4, so it has ______bond lines. Bonding rules (cont.)

. All coefficients and subscripts must be satisfied.

. Ex. 2C2H6- Must draw two molecules each having 2 and 6 hydrogens Changing molecular formulas to structural formulas . All bond lines, subscripts, and coefficients must be satisfied.

. Ex. H2O

Changing structural formulas to molecular formulas . All coefficients and subscripts must be satisfied.

. Ex. H – O – H ―> H2O . Ex. H – Cl H – Cl ―> 2HCl

Types of bonds

. Covalent . Chemical bonding where pairs of electrons are shared . Strongest type of bond (gets stronger as more pairs of electrons are shared) . Polar . Present in water molecules . Because difference between O and H, a bond forms where the O has a partial negative charge and H a partial positive charge

Types of bonds

. Ionic bond . Weak bond formed between two oppositely charged . Type of bonds in salt (NaCl) . . Caused when hydrogen and an electronegative atom bond . Weakest type of bond

. Must contain carbon (C) . Usually associated with living things . Ex. Carbohydrates, lipids, proteins, nucleic acids . What is inorganic???? Chemical Bonds

. What are the two main types of chemical bonds? Chemical Bonds

. The main types of chemical bonds are: . ionic bonds . covalent bonds Chemical Bonds

. Chemical Bonds . The atoms in compounds are held together by chemical bonds. . Bond formation involves the electrons that surround each atomic nucleus. . The electrons that are available to form bonds are called valence electrons. Chemical Bonds

. Ionic Bonds . An ionic bond is formed when one or more electrons are transferred from one atom to another. . An atom that loses electrons has a positive charge. . An atom that gains electrons has a negative charge. . These positively and negatively charged atoms are known as ions. ChemicalSodium atom Bonds (Na) Chlorine atom (Cl) Sodium ion (Na+) ion (Cl-)

Protons +11 Protons +17 Electrons - 1110 Electrons - 1718

Charge +1 0 Charge - 1 0 Chemical Bonds

. Covalent Bonds . Sometimes electrons are shared by atoms instead of being transferred. . Sharing electrons means that the moving electrons actually travel in the orbitals of both atoms. Chemical Bonds

. A covalent bond forms when electrons are shared between atoms. . When the atoms share two electrons, the bond is called a single covalent bond. . When atoms share four electrons it is called a double bond. . When atoms share six electrons it is called a triple bond. Chemical Bonds

. The structure that results when atoms are joined together by covalent bonds is called a . . A molecule is the smallest unit of most compounds. Chemical Bonds

. In a water molecule, each forms a single covalent bond with the oxygen atom. Chemical Bonds

. Van der Waals Forces . When molecules are close together, a slight attraction can develop between the oppositely charged regions of nearby molecules. . call such intermolecular forces of attraction van der Waals forces, after the scientist who discovered them. Chemical Bonds

• Although van der Waals forces are not as strong as ionic bonds or covalent bonds, they can hold molecules together, especially when the molecules are large. Chemical Bonds

. For example, van der Waals forces form between the molecules on the surface of a gecko’s foot and the molecules on the surface of the wall. . The combined strength of all the van der Waals forces allows the gecko to grip the wall.

2-1

. The particles that move around the nucleus of an atom are called . neutrons. . protons. . electrons. . isotopes. 2-1

. The atomic number of a carbon atom is 6. How many neutrons does the isotope carbon-14 have? . 6 . 8 . 12 . 14 2-1

. Which of the following statements about the three isotopes of carbon is true? . They are all radioactive. . They have different numbers of electrons. . They have the same chemical properties but differ in atomic mass. . They have the same number of protons and neutrons. 2-1

. A chemical compound consists of . electrons mixed with neutrons. . two or more elements combined in a definite proportion. . two or more elements combined in any proportion. . at least three elements combined by ionic or covalent bonds. 2-1

. Van der Waals forces are the result of . unequal sharing of electrons. . ionic bonds. . the bonding of different isotopes. . the chemical combination of sodium and chlorine.