Molecules and Compounds Chapter 6 Molecules and Compounds

Physical and Chemical Properties Physical properties: distinguishes one kind of matter from another they can be observed or measured without changing a substance into another substance example: boiling point, color, odor, hardness, density, solubility, and electrical conductivity

Physical and chemical properties describes how a substance unites with another substance to form a new substance two substance unite or two substances break apart new substances from a chemical change have new physical and chemical properties example: rusting, burning

Elements and Compounds Elements are composed of only one type of atom…they are therefore the most basic component of the physical world. Several elements exist naturally as molecules – groups of two or more atoms linked by chemical bonds - an example of this is oxygen

Elements and Compounds Compounds are composed of different types of atoms linked together – compounds are combinations of two or more kinds of elements Example: water (H2O) Composed of two hydrogen atoms and one oxygen atom Compounds can be simple (like water) or complex (like sugar – C12H22O11)

Elements and Compounds Molecular mass: the sum of all the masses of all the atomic masses (atomic mass units – amus) in the compound So…what is the molecular mass of sugar?

Chemical Formulas Molecular formula: gives the name and number of each atom in the molecule example: H2O Structural formula: Shows the arrangement of the atoms in the molecule

Chemical Formulas Empirical formula: shows only the simplest ratio of the atoms in the molecule one empirical formula can represent dozens of different molecules

Chemical Bonding with Electrons When two elements join, their chemical union determines the resulting characteristics of the compound. Bonding is the joining together of elements… it involves mainly the Valence Electrons.

Chemical Bonding with Electrons With the exception of some (i.e. hydrogen) atoms are generally most stable when they have a full octet (8 electrons) in their valence level.

Chemical Bonding with Electrons Graphite and diamonds look very different and yet are both made of carbon!

Chemical Bonding with Electrons They illustrate the fact that the same element can often bond in more than one way.

Chemical Bonding with Elements Atoms fill their valence by bonding with other atoms to form compounds. Atoms react in several ways to achieve this greater stability…

Chemical Bonding with Elements Atoms fill their valence by bonding with other atoms to form compounds. Atoms react in several ways to achieve this greater stability…

Chemical Bonding with Electrons Two ways they achieve stability: Atoms will gain or lose electrons. Some atoms forcibly remove electrons from other atoms. The atom that loses electrons is now stable and the atom that gained is now stable.

Chemical Bonding with Electrons 2. Atoms will share electrons. The goal is the same: a more stable atom with an octet of electrons in their valence shells.

Types of Bonding Covalent Bonding Two atoms have electronegativity close to the same. Also called: Electron Sharing Ionic Bonding One atom has a much greater electronegativity than another The electron is taken away!

Ionic Bonding Formed when one or more electrons are transferred from one atom to another. When an atom gains or loses an electron it is no longer neutral… it is an Ion.

Ions If an atom has more electrons than protons… it is an anion (negative charge) If it has more protons than electrons…it is a cation (positive charge)

Forces between Molecules There are forces between molecules called intermolecular forces. The forces of adhesion and cohesion between the molecules that bind them Differing substances have differing molecular forces – at room temp. molecules of water do not stick together as well as water molecules at zero degrees.

Types of Intermolecular Forces There are three types of intermolecular forces: Dipolar forces London forces Hydrogen forces

Dipolar forces Dipoles are molecules that have positively and negatively charged ends due to the unequal sharing of electrons.