Any substance that contains only one kind of an atom is known as an element. Because atoms cannot be created or destroyed in a chemical reaction, elements such as phosphorus P 4 or sulfur S 8 cannot be broken down into simpler substances by these reactions. Example: Water decomposes into a mixture of hydrogen and oxygen when an electric current is passed through the liquid. Hydrogen and oxygen, on the other hand, cannot be decomposed into simpler substances.
They are therefore the elementary, or simplest, chemical substances - elements. Each element is represented by a unique symbol. The notation for each element can be found on the periodic table of elements. The elements can be divided into three categories that have characteristic properties: metals, nonmetals, and semimetals. Most elements are metals, which are found on the left and toward the bottom of the periodic table.
A handful of nonmetals are clustered in the upper right corner of the periodic table. The semimetals can be found along the dividing line between the metals and the nonmetals. Elements are made up of atoms , the smallest particle that has any of the properties of the element. John Dalton, in , proposed a modern theory of the atom based on the following assumptions.
Atoms of different elements have different weights and different chemical properties. Atoms of different elements combine in simple whole numbers to form compounds. Atoms cannot be created or destroyed. When a compound decomposes, the atoms are recovered unchanged. Metals often react with nonmetals to form ionic compounds. These compounds are composed of positive and negative ions formed by adding or subtracting electrons from neutral atoms and molecules.
Pure Substances When we speak of a pure substance , we are speaking of something that contains only one kind of matter. Pure Substance Element or Compound? Mixtures If we take two or more pure substances and mix them together, we refer to this as a mixture. Heterogeneous mixture A heterogeneous mixture is a mixture in which the composition is not uniform throughout the mixture.
Assuming that the iron and sulfur are simply mixed together, it should be easy to see what is iron and what is sulfur, so this is a heterogeneous mixture. Phase A phase is any part of a sample that has a uniform composition and properties. If it is pure, the substance is either an element or a compound. If a substance can be separated into its elements, it is a compound. If a substance is not chemically pure, it is either a heterogeneous mixture or a homogeneous mixture.
If its composition is uniform throughout, it is a homogeneous mixture. Solution: A Tea is a solution of compounds in water, so it is not chemically pure. It is usually separated from tea leaves by filtration. B Because the composition of the solution is uniform throughout, it is a homogeneous mixture.
A Orange juice contains particles of solid pulp as well as liquid; it is not chemically pure. B Because its composition is not uniform throughout, orange juice is a heterogeneous mixture. A A compact disc is a solid material that contains more than one element, with regions of different compositions visible along its edge.
Hence a compact disc is not chemically pure. B The regions of different composition indicate that a compact disc is a heterogeneous mixture. A Aluminum oxide is a single, chemically pure compound. A Selenium is one of the known elements. Saltwater is a homogeneous mixture, or a solution. Soil is composed of small pieces of a variety of materials, so it is a heterogeneous mixture. Water is a substance; more specifically, because water is composed of hydrogen and oxygen, it is a compound.
Chemistry deals with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds. Chemistry also involves understanding the properties and interactions of individual atoms and molecules for use in larger-scale applications. In chemistry and physics, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic particles, and in everyday as well as scientific usage, "matter" generally includes atoms and anything made up of them, and any particles and objects that act as if they have both rest mass and volume.
However it does not include massless particles such as photons, or other energy phenomena or waves such as light or sound. Matter exists in various states known as phases that are defined by various physical properties, such as state of matter, phase, shape, and density.
The Standard Model of particle physics and the general theory of relativity describe fundamental particles and the fundamental forces acting between them that control the structure and dynamics of matter. Click 'Join' if it's correct. Meredith J. Chemistry 2 months, 2 weeks ago. View Full Video Already have an account? David C. Answer Can you have a mixture of two elements as well as a compound of the same two elements?
Discussion You must be signed in to discuss. Video Transcript Question 70 asks you to apply your knowledge of a mixture and elements. Upgrade today to get a personal Numerade Expert Educator answer! Ask unlimited questions. Test yourself.
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