Atoms and Elements Understanding the World Around Us

Atoms and Elements For most of human history we were able to construct only simple mental models to explain the nature of matter. –What is the sky made of? –What is fire? –What is the world made of? –What is the smallest thing? –What makes things stick together? –What is a dew drop made of? How did it get there?

Atoms and Elements In recent times we have developed much more complex and accurate theories. We can understand the nature of unusual metals, refine carbon based fuels, create complex chemical and polymers. We can even create clothing that sheds water, windows that clean themselves and windows that can tint themselves.

Atoms and Elements How did the modern scientific understanding of matter develop? What technologies have arisen as a result of this scientific knowledge? How does the study of chemical substances in labs translate into practical uses for these substances?

Properties and Changes Does a glass of milk have more in common with a glass of water or a steel girder? Is melting ice the same kind of change as burning paper? How do scientists know the formula of water is H20?

The Nature of Matter The Particle Theory of Matter –All matter is made up of tiny particles. –Each pure substance has its own kind of particle, different from the particles of other pure substances. –Particles attract each other. –Particles are always moving. –Particles at a higher temperature move faster than particles at a lower temperature.

The Nature of Matter Particle theory is an example of a scientific model. Models help scientists to picture or imagine processes in nature that cannot be simply or directly seen.

Classifying Matter Matter can be classified according to its state: solid, liquid, gas, plasma Matter can be classified by whether it is HETEROGENEOUS or HOMOGENOUS. Think back - what do you think these words mean? Matter can also be classified according to its composition - mixture or pure substance.

The Particle Theory Pure substances are always homogenous –Each pure substance contains its own kind of particle. Mixtures contain at least two kinds of particles } If the particles are uniformly scattered the mixture is a homogenous solution } If the particles are not uniformly scattered the mixture is heterogeneous.

Classifying Matter

Changes in Matter Every kind of matter has properties: –Strength –Smell –Taste –Color Properties can be used to identify matter. –Cold –Hard –See through –Slippery –??????

Changes in Matter Properties of matter can change Changes are classified as: Physical Changes Chemical Changes

Physical Changes During a physical change: –No new substance is formed –New properties may appear but the particles are not changed –Changes are temporary - can be reversed. –What are some examples of physical changes that you know?

Chemical Changes During a chemical change: –A new substance, with new properties is always formed. –Difficult or impossible to reverse. –What chemical changes do you know of?

Chemical or Physical Properties Understanding changes in matter depends on knowing the properties of matter. Properties can be physical or chemical

Chemical or Physical Properties Any property that can be observed or measured without forming a new substance is a physical property. –Color –Weight –Density –Size

Chemical or Physical Properties Any property that describes how a substance reacts with another substance when forming a new substance is a chemical property. –Combustability –Stability

Properties Continued Copper reacts with substances in the air to form a green coating Gold has the property of malleability - can be hammered into thin sheets

Density How can we tell the difference between two different metal that look and feel very similar? Look at silver and chromium –Look the same –Feel the same –Both melt at very high temperatures –Let’s measure it’s density

Density 1 cm 3 of silver has a mass of 10.5 grams Density is mass ÷ volume Density of silver is 10.5g ÷ 1cm 3 =10.5g/ cm 3 1 cm 3f of chromium has mass of 7.2 grams 1 cm 3f of chromium has mass of 7.2 grams Density of chromium is 7.2g ÷ 1cm 3 =72.g/ cm 3 Density os a qualitative property