Atoms, Elements, Compounds, and Mixtures Structure of the Atom Atoms are the smallest particles All atoms share the same basic into which matter can be divided structure. Over the years, and still maintain its scientists have designed many characteristics. different models for this structure. Atoms are the building blocks of Each one was the best model at the universe. There are 92 the time, but as new evidence was different kinds of atoms that discovered, the models were occur naturally. revised. These building blocks can be Scientists will probably revise the joined together to create all of current model as more evidence the different kinds of matter we becomes available. can observe. ? What’s inside of an atom? Early Atomic Models “Atoms are The Greek scientist Democritus was indivisible.” the first person to say that all matter is - Democritus made of atoms, but he also said that atoms are indivisible. Atoms of an element are alike. In the early 1800’s, the English scientist John Dalton developed his Atomic Theory of Matter. It said four things: (1) All matter is made of Different elements atoms. (2) Atoms of an element are alike. (3) have different atoms. Atoms of different elements are different. (4) Atoms of different elements join together to + = make compounds. Positively- charged matrix Atoms join to make compounds. - John Dalton Negatively- In the late 1800’s, J. J. Thomson charged electron discovered that atoms were made of smaller particles. He discovered the - J. J. Thomson electron and devised the “chocolate-chip cookie” model of the atom. Recent Atomic Models Protons are in the nucleus. In the early 1900’s, scientists - Rutherford discovered the positively-charged proton. In 1911, Rutherford discovered the nucleus of the atom, where protons are located. Atoms are mostly empty space. Niels Bohr changed Rutherford’s model in Electrons orbit the nucleus. 1913. Bohr said that electrons move around - Niels Bohr the nucleus in fixed energy levels. Electrons can move from one energy level to another. Bohr’s model has been called the “solar system” model of the atom. Negative electron cloud The current model of atomic structure is called the “electron cloud” Neutral neutrons are model. Electrons move within an in nucleus with positive protons. energy level in an ever-changing path, - electron cloud not a fixed orbit. Neutrons bond with model protons in the nucleus. Atomic Number and Mass Number All atoms of an element have the Atoms of the same element may same number of protons, and have different numbers of different elements have different neutrons. Atoms with extra or numbers of protons in their missing neutrons are called atoms. isotopes. The atomic number of an atom is An atom’s mass number is the the number of protons it has. If number of protons plus neutrons. the atom is neutral, the atomic Different isotopes of an element number is also the number of have different mass numbers. electrons. Mass number of this Atomic number of neutral atom is 14. This is this neutral atom = the sum of the protons plus 6. This means neutrons. Since there are that it has 6 protons 6 protons, there must be 14 and 6 electrons. - 6 = 8 neutrons. (protons are blue, electrons are yellow, and neutrons are green) Elements An element is matter that is At room temperature, most made of only one kind of atom. elements are solids, although a All of the atoms of an element few are liquids and some are are alike. There are 92 gases. naturally occurring elements. Chemical symbols are Elements can be identified by abbreviations for the names of their properties. Some elements. You can also use a properties are color, texture, chemical symbol to represent one density, malleability, ductility, atom of an element. Chemical ability to dissolve in water, and symbols are the same all over the ability to conduct heat or world, no matter what language is electricity. spoken. Na Chemical symbol for the Chemical symbol for the element Chlorine, used element Sodium, used in in bleach and water sodium vapor lamps. treatment. Cl Compounds The atoms of most elements are Compounds are separated into two very reactive. They chemically groups, depending on how their join together with atoms of other atoms are joined: (1) Molecular elements to form compounds. compounds are made of atoms that The properties of compounds are share electrons. (2) Ionic compounds different than the properties of are made of atoms that gain or lose the elements that make the electrons. compound. Chemical formulas represent When elements join to make compounds. They show the kind compounds, they always join in and number of atoms in the H is symbol for the same proportion. H2O is water, not HO or H3O ! O is symbol for compound. N is symbol for Nitrogen NH3 Hydrogen H is symbol for Hydrogen H2O Oxygen No subscript No subscript means one Subscript 3 Nitrogen means there are Subscript 2 means one 3 Hydrogen atoms means that there Oxygen atom atoms are 2 Hydrogen atoms Water Ammonia molecule Molecule Mixtures Mixtures are made when there are at least two different kinds of atoms that are in the same This coffee is a place but are not chemically mixture. combined. A mixture can be made with any proportion of ingredients, but a compound must be made in only one certain way. This cake is a mixture. Components of a mixture keep their own properties, but those of a compound do not. Components of a mixture are not chemically combined, so they can be separated by This basket of fruit is also a mixture. physical means like filtering or evaporation. Types of Mixtures A homogeneous mixture is the same throughout. All parts of the mixture have the same proportion of ingredients. This cookie is A heterogeneous mixture is heterogeneous. different in different parts. Different regions of this kind of mixture have different proportions Soft drinks are of the ingredients. homogeneous mixtures. An alloy is a homogeneous mixture of metals. The crayons in the The alloy these keys are pail make a made of is a homogeneous heterogeneous mixture. mixture. The milk is homogeneous. The gelatin mold is a heterogeneous mixture.
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