Matter and Energy: What are atoms?

Transcription

1 Matter and Energy: What are atoms? By Encyclopaedia Britannica, adapted by Newsela staff on Word Count 546 Level 820L An illustration of an atom. The nucleus, containing neutrons and protons, is at the center. Circling around it are electrons. Image from: Pixabay. The tiny particles called atoms are the basic building blocks of all matter. Atoms can be combined with other atoms to form molecules. However, they cannot be divided into smaller parts by ordinary means. The word atom derives from the Greek word "atomos," which means indivisible. Something that is indivisible cannot be divided. The ancient Greeks were the first to think of the atom as the basic unit of all matter. But it was not until the 1800s that scientists began to understand how atoms work. This article is available at 5 reading levels at 1

2 Atoms Made Up Of Subatomic Particles Each individual atom is made up of smaller particles called electrons, protons and neutrons. These are known as subatomic particles. At the center of each atom is the nucleus. The nucleus consists of protons and neutrons. Protons carry a positive electrical charge, while neutrons carry no electrical charge. Together, protons and neutrons are called nucleons. Surrounding the nucleus is a cloud of negatively charged electrons. Scientists believe that subatomic particles are themselves made up of even smaller substances. These substances are called quarks and leptons. This article is available at 5 reading levels at 2

3 Atomic Number Determines What Kind Of Atom It Is The most important thing to know about an atom is how many protons it has in its nucleus. This is known as its atomic number. The atomic number determines what kind of atom it is. Every atom is associated with a certain chemical element. An atom is the smallest unit of an element, and each chemical element has its own atomic number. For instance, hydrogen has an atomic number of 1. That's because every hydrogen atom has one proton in its nucleus. No other element has an atomic number of 1. Each atom also has a mass number and an atomic weight. The mass number is equal to the total number of protons and neutrons in an atom. The atomic weight is equal to the mass number divided by a certain number that scientists have come up with. The mass number and atomic weight are very similar. For example, carbon's mass number is 12. Its atomic weight is Some atoms have the same atomic number, but different mass numbers. These kinds of atoms are called isotopes. For example, Carbon-12 is the ordinary form of carbon. It has six protons and six neutrons in each atom. Carbon-14 is an isotope with six protons and eight neutrons in each atom. It still has six protons. If it did not have six protons, it would not be carbon. An ordinary atom has an equal number of protons and electrons. Therefore its positive and negative charges are balanced. But sometimes atoms lose or gain electrons. This can happen through chemical reactions or by colliding into other particles. Ordinary atoms that either gain or lose electrons are called ions. If an ordinary atom loses an electron, it becomes a positive ion. If it gains an electron, it becomes a negative ion. This article is available at 5 reading levels at 3

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5 Quiz 1 Read the summary below. Choose the answer that BEST fits into the blank to complete the summary. Atoms are the tiny building blocks of everything in nature. The number of protons an atom has is called its atomic number, which decides what kind of atom it is. Changes in the number of neutrons make an isotope, and changes to the number of electrons make an ion. They are made up of subatomic particles called protons, electrons and neutrons. They are made up of only negative and neutral electrical charges in the nucleus. They are made up of a nucleus with a surrounding cloud of neutrons and protons. They are made up of quarks and leptons that are divided into even smaller particles. 2 Read the following paragraph from the article. An ordinary atom has an equal number of protons and electrons. Therefore, its positive and negative charges are balanced. But sometimes atoms lose or gain electrons. This can happen through chemical reactions, or by colliding into other particles. Ordinary atoms that either gain or lose electrons are called ions. If an ordinary atom loses an electron, it becomes a positive ion. If it gains an electron, it becomes a negative ion. Which answer choice BEST describes the structure of the paragraph? chronological order compare and contrast cause and effect problem and solution This article is available at 5 reading levels at 5

6 3 Which statement from the section "Atoms Made Up Of Subatomic Particles" suggests that there might be particles tinier than protons, electrons and neutrons? Together, protons and neutrons are called nucleons. Scientists believe that subatomic particles are themselves made up of even smaller substances. The tiny particles called atoms are the basic building blocks of all matter. These are known as subatomic particles. 4 Based on information in the article, which of these statements is TRUE? The atomic number is determined by how many protons are in the nucleus. The atomic weight is determined by how many electrons are in the nucleus. The atomic number is determined by dividing the protons by the neutrons. The atomic weight is determined by dividing the neutrons by the electrons. This article is available at 5 reading levels at 6

7 Answer Key 1 Read the summary below. Choose the answer that BEST fits into the blank to complete the summary. Atoms are the tiny building blocks of everything in nature. The number of protons an atom has is called its atomic number, which decides what kind of atom it is. Changes in the number of neutrons make an isotope, and changes to the number of electrons make an ion. They are made up of subatomic particles called protons, electrons and neutrons. They are made up of only negative and neutral electrical charges in the nucleus. They are made up of a nucleus with a surrounding cloud of neutrons and protons. They are made up of quarks and leptons that are divided into even smaller particles. 2 Read the following paragraph from the article. An ordinary atom has an equal number of protons and electrons. Therefore, its positive and negative charges are balanced. But sometimes atoms lose or gain electrons. This can happen through chemical reactions, or by colliding into other particles. Ordinary atoms that either gain or lose electrons are called ions. If an ordinary atom loses an electron, it becomes a positive ion. If it gains an electron, it becomes a negative ion. Which answer choice BEST describes the structure of the paragraph? chronological order compare and contrast cause and effect problem and solution This article is available at 5 reading levels at 7

8 3 Which statement from the section "Atoms Made Up Of Subatomic Particles" suggests that there might be particles tinier than protons, electrons and neutrons? Together, protons and neutrons are called nucleons. Scientists believe that subatomic particles are themselves made up of even smaller substances. The tiny particles called atoms are the basic building blocks of all matter. These are known as subatomic particles. 4 Based on information in the article, which of these statements is TRUE? The atomic number is determined by how many protons are in the nucleus. The atomic weight is determined by how many electrons are in the nucleus. The atomic number is determined by dividing the protons by the neutrons. The atomic weight is determined by dividing the neutrons by the electrons. This article is available at 5 reading levels at 8