B.3 – B.4 In which you will learn about: Pure substances Mixtures Atoms, molecules, compounds, elements

B.3 MIXTURES AND SOLUTIONS

Types of Matter Mixture - Variable combination of 2 or more pure substances. Heterogeneous – visibly separate materials Homogeneous (solution)– Same throughout

Types of heterogeneous mixtures Suspension: solid particles are large enough to settle out or can be separated by using filtration – Ex: water and coffee grounds – Ex: water and pepper flakes Colloid: particles smaller than a suspension (don’t settle out) and may cause water to appear cloudy (but can’t see individual particles) – Ex: whole or low-fat milk Tyndall Effect: exhibited by both suspensions and colloids—when light is scattered by particles in a mixture

Homogeneous Mixtures Particles that are far smaller than colloidal particles are often dissolved into a mixture Homogeneous mixtures (solutions) do NOT exhibit the Tyndall Effect Solvent: the dissolving agent Solute: the dissolved substance

Mixture Comparison Mixture TypeAppearanceParticles Settle Out? Tyndall Effect? SuspensionLarge particles suspended in solvent, visible to the eye Yes ColloidMedium particles not visible to the eye, but mixture appears cloudy NoYes SolutionSmall particles, invisible to the eye and microscope, and mixture appears clear No

B.4 Particulate View of Water

Macroscopic v. Microscopic In chemistry, we make observations in the lab on the macroscopic level We then explain our observations at the microscopic level, or particulate level. This explains the big world stuff based on the interactions of atoms and molecules.

Pure Substance = ONE material CHEMICAL ELEMENT - CHEMICAL ELEMENT - – pure substances that cannot be decomposed by ordinary means to other substances. Sodium Bromine Aluminum

The Language of Chemistry The elements, their names, and symbols are given on the PERIODIC TABLE The elements, their names, and symbols are given on the PERIODIC TABLE How many elements are there? How many elements are there? 117 elements have been identified 82 elements occur naturally on Earth 82 elements occur naturally on Earth Examples: gold, aluminum, lead, oxygen, carbon 35 elements have been created by scientists35 elements have been created by scientists Examples: technetium, americium, seaborgium

The Periodic Table Dmitri Mendeleev ( )

Glenn Seaborg ( ) Discovered 8 new elements. Discovered 8 new elements. Only living person for whom an element was named. Only living person for whom an element was named.

Copper atoms on silica surface. An ATOM is the smallest particle of an element that has the chemical properties of the element. An ATOM is the smallest particle of an element that has the chemical properties of the element. Distance across = 1.8 nanometer (1.8 x m)

An atom consists of a nucleus nucleus – (of protons and neutrons) electrons in space about the nucleus. electrons in space about the nucleus. The Atom Nucleus Electron cloud

The red compound is composed of nickel (Ni) (silver) carbon (C) (black) hydrogen (H) (white) oxygen (O) (red) nitrogen (N) (blue) CHEMICAL COMPOUNDS are pure substances composed of atoms and so can be decomposed to those atoms.

Compounds – composed of 2 or more elements in a fixed ratio – properties differ from those of individual elements – EX: table salt (NaCl) – NOT reactive like Na, and NOT poisonous like Cl 2

A MOLECULE is any two or more atoms chemically bonded together. MOST molecules are compounds, like those shown below. Composition of molecules is given by a MOLECULAR FORMULA H2OH2OH2OH2O C 8 H 10 N 4 O 2 - caffeine

BUT SOME ELEMENTS EXIST AS DIATOMIC MOLECULES MEMORIZE: BrINClHOF These elements only exist as PAIRS. Note that when they combine to make compounds, they are no longer elements so they are no longer in pairs!

Matter Flowchart – To Sum it All Up MATTER Can it be physically separated? Homogeneous Mixture (solution) Heterogeneous MixtureCompound MIXTUREPURE SUBSTANCE yesno Can it be chemically decomposed? noyes Is the composition uniform? noyes ColloidsSuspensions Element

HOMEWORK QUESTIONS 1) Match each description below with the following microscopic pictures. More than one picture may fit each description. A picture may be used more than once or not used at all. a)A gaseous compound b)A mixture of two gaseous elements c)A solid element d)A mixture of a gaseous element and a gaseous compound

HOMEWORK CONT’D 2) How are heterogeneous and homogeneous mixtures different? 3) Identify each of the following materials as a solution, a suspension, or a colloid. – A medicine accompanied by instructions to “shake before using.” – Italian salad dressing – Mayonnaise – A cola soft drink – An oil-based paint – milk

MORE HOMEWORK 4)You notice beams of light passing into a darkened room through the blinds on a window. Does this demonstrate that air in the room is a solution, a suspension, or a colloid? Explain. 5) Suppose you have a clear, red liquid mixture. A beam of light is observed as it passes through the mixture. Over a period of time, no particles settle to the bottom of the container. Classify this mixture as a solution, a colloid, or a suspension and provide evidence to justify your choice.

OMG, EVEN MORE HW 6) Define the term pure substance and give two examples. 7) Classify each of the following substances as an element or a compound: – CO – Co – HCl – Mg – NaHCO 3 – NO – I 2