Chapter 7 Atoms, Elements, Compounds and Mixtures
7.1 Structure of an Atom • OBJECTIVES: • Summarize how models of the atom have changed. • Name and describe parts of an atom • Calculate the number of protons, neutrons and electrons in an atom given its mass number.
Structure of an Atom • YOU have learned that all matter in the universe is made up of tiny particles. • A glass of water has many water particles, each too small to see. • If you could see them, what would they look like? • What makes them different from the particles of other kinds of matter?
Atoms and Elements • Water particles can actually be divided into even smaller pieces of matter. • These particles are examples of the most basic units of matter called atoms. • Atomscan't be broken down into smaller pieces by any common methods of separating matter.
Atoms and Elements • Atoms are the building blocks of the universe. • Scientists have identified nearly 100 different kinds of naturally occurring atoms. • Each kind of atom has unique properties and is called an element. • An atom of an element can't be broken down and retain its properties.
Atoms and Elements • The particles of matter can be made of single atoms, two or more atoms of the sameelement, or two or more atoms of different elements. • This water particle is made up of three atoms, two of hydrogen and one of oxygen.
Models of the Atom • All atoms share the same basic structure. • During the past 200 years, scientists have proposed different models for this structure. • Each model was the best one for its time. • With new observations or experiments, however, the model had to be changed. • http://highered.mcgraw-hill.com/sites/dl/free/0078600499/164155/00044672.html
Dalton's Model • * In the early 1800s, John Dalton performed experiments with gases. • His results convinced him that matter was made up of tiny particles. • …and that each element must be made of its own unique kind of particle and that these particles combine in simple ways.
Dalton's Model • Dalton called these basic particles atoms and pictured them as tiny, solidspheres.
Dalton's Model Based on his experiments, Dalton developed a theory of the structure of matter. His theory contained four main concepts: • All matter is composed of tiny, indivisible particles called atoms. • Atoms of each element are exactly alike. • Atoms of different elements have different masses. • Atoms of different elements can join to form compounds.
Thomson's Model • At the end of the 1800s, J. J. Thomsondiscovered that atoms were not just simple, solid spheres and contained even smaller, subatomic particles. • The subatomic particles Thomson discovered were very small and negatively charged. • Thompson called them electrons.
Thomson's Model • Thomson knew that atoms are electrically neutral. Therefore, he reasoned, an atom must contain enough positive charge to balance the negative charge of the electrons. • Thomson developed an atomic model in which electrons were stuck into a positively charged sphere. • A positive charge in the substance of the sphere balanced the electrons' charge .
Rutherford's Model • By the early 1900s, scientists knew that the positive charge of an atom comes from subatomic particles called protons. • A proton is a positive particle with a mass much greater than that of an electron. • At that time, scientists hypothesized that electrons and protons were evenly scattered throughout an atom.
Rutherford's Model • In 1911 , Ernest Rutherfordset out to test this theory. • After experimenting with a beam of positively charged light, he concluded that the protons are concentrated in a small area at the center of the atom. • He called this region thenucleus.
Rutherford's Model • In his model, an atom is mostly empty space. The nucleus is tiny compared to the whole atom, but it contains nearly all the atom's mass. • http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf
Bohr's Model • NielsBohr modified Rutherford's model in 1913. He proposed that each electron in an atom has a fixed amount of energy. • This energy keeps an electron moving around the nucleus within a specific region called an energy level. • In Bohr's model, energy levels surround the nucleus in rings or shells, like the layers of an onion.
Bohr's Model • In the Bohr Model, an electron can move from one energy level to another just as you can climb up or down a ladder, by absorbing or releasing a specific amount of energy. • Just as you can't be between rungs on a ladder, an electron can't be between energy levels. • Bohr's model has been called the ‘planetary model’ as it compares electrons to planets and the nucleus to the sun.
Electron Cloud Model • Today scientists know that electrons do not actually orbit the nucleus as in Bohr's planetary model. • The electron cloud model is now used to describe atoms. • In this model, electrons dart about within an energy level in an ever-changing path. • Most of this path falls into a region called an electron cloud. • At any given time, there is a high probability that the electron exists in the electron cloud.
Electron Cloud Model http://www.youtube.com/watch?v=zYeRSgiypbc • The idea of an electron cloud is not so strange. You have probably seen the blur of a fan when it spins at high speed. • The fast-moving blades appear to fill the space between them, just as fast-moving electrons seem to fill the space around the nucleus. • The paths of an atom's electrons account for nearly all of its volume.
Inside the Nucleus • As scientists learned more about atomic structure, they found that the nucleus is more complicated than they had thought. • In 1932, scientists showed that most atomic nuclei contain a third kind of subatomic particle, called a neutron. • A neutron has about the same mass as a proton but has no electrical charge. • An atomic nucleus is a positively charged, tightly-packed cluster of protons and neutrons.
Atomic Numbers and Isotopes • All atoms of an element contain the same number of protons. • This number, called the atomic number, identifies an element. • Sodium, for example, has an atomic number of 11.
Atomic Numbers and Isotopes • If all iron atoms contain 26 protons, what is the atomic number of iron? • The atomic number also represents the number of electrons in an atom. • Remember that an atom is electrically neutral. Thus the number of negative particles must equal the number of positive particles.
Atomic Numbers and Isotopes • As you may recall, Dalton hypothesized that all atoms of an element are exactly alike. Today scientists know that he was not completely correct. • Atoms of the same element do have the same number of protons and electrons, but they may differ in the number of neutrons they contain. • Atoms of the same element with different numbers of neutrons are calledisotopes.
Mass Number and Atomic Mass • Almost every atom contains one or more neutrons in it’s nucleus. • The number of neutrons does not affect the charge of an atom, but it does affect its mass. • The total number of protons and neutrons in an atom is called its mass number. • The mass number helps to distinguish one isotope from another. • What is the difference between carbon-12 and carbon-14?
Brain Pop! http://www.brainpop.com/science/matterandchemistry/isotopes/preview.weml
Check & Explain pg. 163 Answer Question 4
Draw one of each model of a neon atom. Dalton, Thomson, Rutherford and Bohr
7.2 Elements Objectives • Describe what elements are. • Give examples of common elements. • Make a model that relates the particle model to a familiar property of matter.
Elements • High in the Rocky Mountains or on the streets of New York City, the oxygen in the air you breathe is the same. • The air is different, but the oxygen atoms in both places have the same properties. All oxygen atoms have eight protons and eight electrons.
Elements • Oxygen is an element. • As you have learned,elements are the basic kinds of matter in the universe. • An element is a substance made of just one kind of atom. • It cannotbe broken down or changed by chemical means.
Elements and Matter • Even though all matter is made up of elements, only a few elements exist in nature in their pure form. • You may remember that the oxygen and nitrogen in air are elements. • Diamond is a natural form of the element carbon. • Occasionally pure deposits of silver, gold, or copper are found.
Elements and Matter • You would probably not recognize most elements in their pure form because most elements in nature are combined with other elements.
Elements and Matter • Of the more than 100 known chemical elements, only about 30 play an important role in your daily life. • About 18 elements do not occur in nature. They are created in laboratories and known as syntheticelements.
Properties of Elements • The properties used to describe the elements in their pure forms include luster, texture, color, density and the ability to conduct electricity. • Elementsdiffer in how they react with other elements. Most elements are solids but some are gases and others are liquids.
Chemical Symbols • Chemists use symbols to represent the names of elements (and atoms). • A chemical symbol is one or two letters taken from the name of the element. • In some cases, the symbol is derived from the element's name in a language other than English. • The symbol for gold, Au, comes from aurum, the Latin word for gold.
Chemical Symbols • Symbolsform a kind of universal chemical shorthand. Ca means calcium to chemists in Japan, Mexico, Kenya, India, and everywhere else.
Check & Explain pg. 167 Answer questions 1 & 2 Page 167
7.3 Compounds Objectives • Describe the properties of a compound. • Give examples of common compounds. • Define operationally the composition of a compound by writing its chemical formula.
Compounds • Nearly all the products you use are made of more than one element. • The clothes you wear, the food you eat for breakfast, and the toothpaste you use to brush your teeth are all combinations of elements. • Almost everything you can think of is made up of some combination of elements.
Defining Compounds • There are millions of compounds in, on, and around the earth. Many compounds are found in living things. • Compounds also make up most of the nonliving world. • Water is a compound.
Defining Compounds • How are compounds formed? • Many are createdby geologic processes deep in the earth. • Organisms must manufacture compounds to stay alive. Plants are always making the compound glucose. • Many products you buy are made of compoundsthat aren't found in the natural world. • For example, if you look at the list of ingredients on food packages you will probably see some compounds you don't recognize. People create these compounds in factories and chemical plants.
Properties of Compounds • The properties of a compound are differentfrom those of the elements that make it up. • Hydrogen and oxygenare both gases. but they combine to form water. • The elements that make it up always combine in a specific proportion. • Carbon dioxide is two parts oxygen and one part carbon (CO2).
Properties of Compounds Study the text and photographs on pg. 169 Answer on a separate piece of paper: -What is the difference between the compounds carbon dioxide and carbon monoxide? -How does the compound sodium chloride differ from the elements sodium and chloride? -What compound is common in rocks, and what elements does the compound contain? -What is the natural form of calcium carbonate, and what three elements make it up?