chemistry notes

Unit 1© Fall 2005, Pflugerville ISD, 7th Grade

Chemistry Notes

6th Grade Science 2010-2011


Elements, Compounds, and Mixtures

What Do You Think?

How is an element different from a

compound?


Answer

An element is made up of only one pure substance, and a compound is composed of two or more elements that are chemically combined.

Gold

Water

http://www.nbmg.unr.edu/slides/water/5.htm

http://www.worldofrockhounds.com/huge-gold-nugget-sm.JPG


Elements

An element is a pure substance that cannot be separated into simpler substances by physical or chemical means.


Elements

A pure substance is a substance in which every particle of that element is the same. – Example: Every particle in a 5g gold

nugget is like every other particle of gold, no matter where they are found.

http://www.libertarian.nl/NL/archives/01-gold-bar.jpg


Elements

Every element has a unique set of properties.

The Periodic Table of Elements is arranged according to these properties.


Elements

Every element has a unique set of properties.

Some physical properties that are used to classify elements are boiling point, melting point, color, and density.


Elements

Chemical properties used to separate elements from each other include reactivity with acids, or reactivity with oxygen.


Elements Are Grouped

Some elements are shiny, and can conduct thermal energy. They are all grouped together on the left hand side of the Periodic Table. They are called metals. Not all metals are exactly alike, but they do have some properties in common.


Elements

Elements Can Be Identified By Categories

If you know the category, you know the properties.

Try this!

1. Share with your class how CDs can be classified by

categories?

2. How can dogs be classified by categories?


Elements

Elements are

identified by 3 main categories

• Metals

• Nonmetals

• Metalloids


Elements

Metals are elements that are usually shiny and good conductors of electricity and heat.

Metals


Elements

Metals are also malleable (can be hammered into thin sheets).

Metals


Elements

• Metals are ductile, or can be drawn into thin wires.

• Metals are located to the left of the “zig zag line” on the Periodic Table.


Elements

• Examples: Iron (Fe) and Copper (Cu).

http://www.flamo.net/crystals/iron.jpg http://resourcescommittee.house.gov/subcommittees/emr/usgsweb/materials/copper.html


Elements

Click below to see properties of Metals.

http://www5.unitedstreaming.com/index.cfm


Elements

Nonmetals

• Usually dull and poor conductors of heat and electric current.

• Tend to be brittle and unmalleable.


Elements

Nonmetals

• Nonmetals are located to the right of the “zig zag line” on the Periodic Table.


Elements

Nonmetals

• Examples: Neon (Ne) and Carbon (C)

www.neonstreet.com/ sign2.html reluctant-messenger.com/ diamond_sutra.htm


Elements

Click below to see properties of Nonmetals



Elements

Metalloids

Share properties of both metals and nonmetals.

• Can be shiny or dull.• Somewhat malleable and

ductile.


Elements

• Metalloids touch the “zig zag line” on the Periodic Table.

• Examples:

Silicon (Si) Arsenic (As).


Elements

Click below to see properties of metalloids.



Let’s Review!

- 1 -

Describe some physical properties of the element iron.

http://neil.fraser.name/news/2004/05/22/


Answer

Physical properties include:

1. Melting Point: 1535 °C

2. Density: 7.9 g/cm3

3. Iron has the ability to conduct heat and electrical current.


Let’s Review

- 2 -

What is an example of a metal that is very

malleable, shiny, and is used often in kitchens?


Answer

Aluminum Foil


Compounds

What do salt, sugar, baking soda, and

water have in common?

What Do You Think?


Compounds

A compound is a pure substance composed of two or more elements that are chemically combined.

Familiar Compound

Compound Elements Combined

Table Salt Sodium and Chlorine

Water Hydrogen and Oxygen

Sugar Carbon, Hydrogen, and Oxygen

Carbon Dioxide Carbon and Oxygen

Baking Soda Sodium, Hydrogen, Carbon, and Oxygen


Compounds

Properties of Compounds

• Compounds, like elements, can be identified by their own physical and chemical properties.

• What are some examples of physical and chemical properties?


Compounds

Each compound has different properties than the elements that make them up.

Water Hydrogen Oxygen

Melting Point 0°C -259.14 °C -218.4 °C

Boiling Point 100 °C -252.87 °C -183.0 °C

Density 1.0 g/cm3 0.08988 g/cm3 1.429 g/cm3

State at Room Temperature Liquid Gas Gas


Compounds

Compounds are Composed of Elements.

The compound Water is composed of Hydrogen and Oxygen chemically bonded together.


Compounds

Compounds are Composedof Elements.

• The compound Ammonium is composed of Nitrogen and Hydrogen chemically bonded together.


Compounds

Click below to see a video clip of sodium metal and chlorine gas being combined.


Let’s Review!

- 1 -

What is the difference between an element and a

compound?


Answer

• An element is a pure substance that cannot be separated into simpler means by physical or chemical means.

• A compound is a pure substance composed of two or more elements that can be broken into simpler substances by a chemical change.


Compounds

Make a Venn diagram comparing and contrasting elements and compounds.

Elements Compounds



Pre-AP Extensions for Chapter 2

• Mixtures are combinations of two or more elements that are not chemically combined.

• Mixtures can be separated into 2 types: homogenous mixtures and heterogenous mixtures.



Homogenous Mixtures

• A homogenous mixture is a mixture of two or more substances that is completely uniform in composition.

• Homogenous mixtures can be separated by physical means, but it is often difficult to do.

• Examples include salt water, kool aid, and air.



Heterogenous Mixtures

• A heterogenous mixture consists of many different items, which are often not easily sorted or separated, though they are clearly distinct.

• Examples include oil and water mixed together, sand or gravel, and even chocolate chip cookies!



Websites to Visit

• Percent Calculations in a Mixture

• Chromatography Mixtures Lab


Introduction to the Periodic Table

What Do You Think?

How do scientists use physical properties to

arrange elements on the periodic table?



Dimitri Mendeleev discovered a pattern to the elements in the periodic table in 1869.

www.astrosurf.org/lombry/ quantique-histoire.htm



He simply wrote the names of all of the elements on cards, along with some of their properties.



• Mendeleev tried arranging his cards based on different properties like color, density, melting point, and atomic mass.

• He found that by arranging the elements by increasing atomic mass, he found many other properties that fit a pattern.



Mendeleev found that by arranging the elements by increasing atomic mass, similar physical and chemical properties repeated in every 8th element.

This is called periodic, or having a regular, repeating pattern.

Can you think of anything else that is periodic?


Let’s Review!

- 1 -

Why was Mendeleev so important in the study of the

periodic table?


Answer

• Mendeleev was responsible for arranging the periodic table by increasing atomic mass.

• This arrangement organizes the table making it easier for us to use.



What Do You Think?

How do scientists use physical properties to

arrange elements on the periodic table?



Elements are classified on the periodic table based on their properties.

• Like we learned in Chapter 2, we classify them as metals, nonmetals, and metalloids.



Remember that metals are shiny, ductile, malleable, and are good conductors of thermal energy and electrical current.

Metals

http://shawnee.noacsc.org/highschool/departments/teachers/pages/mikel/periodictable.html



Metals are located to the left of the “zig zag” line on the periodic table.

Metals



Go.hrw.com

Physical Properties of Metals



Go.hrw.com

Chemical Properties of Metals



Remember also that nonmetals are not shiny and are poor conductors of thermal energy and electric current.

Nonmetals




Nonmetals are found to the right of the “zig zag” line on the periodic table.


Nonmetals



Go.hrw.com

Physical and Chemical Properties of Nonmetals



Metalloids are elements that have properties of both metals and nonmetals.

Metalloids




Metalloids border the “zig zag” line on the periodic table.

Metalloids



Go.hrw.com

Physical and Chemical Properties of Metalloids


Let’s Review!

- 1 -

Use the properties of metalloids to explain their position on the

periodic table.


Answer

• Metalloids are located between metals and nonmetals because they have properties in between metal and nonmetals.




• There are trends in Metallic and Nonmetallic Character that we can see on the periodic table.

• Metallic character is strongest for the elements in the leftmost part of the periodic table, and tends to decrease as we move to the right in any period.



• Within any group of elements (columns), the metallic character increases from top to bottom . This general trend is not necessarily observed with the transition metals.




http://wine1.sb.fsu.edu/chm1045/notes/Periodic/Metals/Period06.htm

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