Classifying Matter Elements, Compounds or Mixtures

Overview Structure of an atom Borh’s Model Subatomic particles Nucleus Electron shells/orbitals Elements, Compounds, Mixtures

Structure of the Atom Are there pieces of matter that are smaller than atoms? Atoms are composed of subatomic particles called electrons, protons, and neutrons. Scientists call the center region of the atom the nucleus. The nucleus in a cell is a thing. The nucleus in an atom is a place where you find protons and neutrons. The electrons are always found whizzing around the center in areas called shells or orbitals. Electrons have a negative charge and protons have a positive charge whereas neutrons have no charge. They are neutral. Due to the presence of equal number of negative electrons and positive protons, the atom as a whole is electrically neutral.

Bohr’s Model In order to explain the stability of an atom, Neils Bohr gave a new arrangement of electrons in the atom in According to Neils Bohr, the electrons could revolve around the nucleus in only 'certain orbits' (energy levels), each orbit having a different radius.

Orbitals  The center of the atom is called the nucleus.  Electrons are found in areas called shells. A shell is sometimes called an energy level.  Shells are areas that surround the center of an atom.  Each of those shells has a name (K, L, M, N, O, P, Q).  There are a couple of ways that atomic shells are described. The most general terms are basic regions where you find electrons. Chemists use the letters K, L, M, N, O, P, and Q. The "K" shell is the one closest to the nucleus, and "Q" is the farthest away.

Elements  Elements are the building blocks for all matter.  As you probably know, the periodic table is organized like a big grid. The elements are placed in specific locations because of the way they look and act. If you have ever looked at a grid, you know that there are rows (left to right) and columns (up and down). The periodic table has rows and columns, and they each mean something different.  We sometimes use the terms atom and element to mean the same thing. Remember that atom is the general term. Everything is made of atoms. The term element is used to describe atoms with specific characteristics. There are almost 120 known elements.

Compounds  Compounds are groups of two or more elements that are bonded together. You have also seen us use the word molecule.  Molecule is the general term used to describe atoms connected by chemical bonds. Every combination of atoms is a molecule. Compounds happen with atoms from different elements. So, all compounds are molecules, because they have bonds between the atoms, like in water (H 2 O).  However, not all molecules are compounds because sometimes the atoms are of the same element. Hydrogen gas (H 2 ) is a good example of a molecule that is not a compound.

Compounds  The process of naming compounds is just a set of rules. When you have two different elements, there are usually only two words in the compound name. The first word is the name of the first element. The second word tells you the second element and how many atoms there are in the compound. The second word usually ends in IDE. That's the suffix. When you are working with non-metals like oxygen (O) and chlorine (Cl), the prefix (section at the beginning of the word) of the second element changes based on how many atoms there are in the compound.

Mixt ures  Mixtures are absolutely everywhere you look. Most things in nature are mixtures. Look at rocks, the ocean, or even the atmosphere. They are all mixtures, and mixtures are about physical properties, not chemical ones. That statement means the individual molecules enjoy being near each other, but their fundamental chemical structure does not change when they enter the mixture.  Scientists say that solutions are homogenous mixtures. Everything in a solution is evenly spread out and mixed together.  Let's compare sugar in water (H 2 O) to sand in water. Sugar dissolves and is spread throughout the glass of water. The sand sinks to the bottom. The sugar-water could be considered a solution. The sand-water combination is a heterogeneous mixture.  ompoundsandmixtures/ ompoundsandmixtures/