Science is a systematic discipline that builds and organises knowledge in the form of testable hypotheses and predictions about the universe. Modern science is typically divided into two or three major branches: the natural sciences (e.g., physics, chemistry, and biology), which study the physical world; and the social sciences (e.g., economics, psychology, and sociology), which study individuals and societies. Applied sciences are disciplines that use scientific knowledge for practical purposes, such as engineering and medicine. While sometimes referred to as the formal sciences, the study of logic, mathematics, and theoretical computer science (which study formal systems governed by axioms and rules) are typically regarded as separate because they rely on deductive reasoning instead of the scientific method or empirical evidence as their main methodology. (Full article...)
A chemical element is a chemical substance whose atoms all have the same number of protons. The number of protons is called the atomic number of that element. For example, oxygen has an atomic number of 8: each oxygen atom has 8 protons in its nucleus. Atoms of the same element can have different numbers of neutrons in their nuclei, known as isotopes of the element. Two or more atoms can combine to form molecules. Some elements form molecules of atoms of said element only: e.g. atoms of hydrogen (H) form diatomic molecules (H2). Chemical compounds are substances made of atoms of different elements; they can have molecular or non-molecular structure. Mixtures are materials containing different chemical substances; that means (in case of molecular substances) that they contain different types of molecules. Atoms of one element can be transformed into atoms of a different element in nuclear reactions, which change an atom's atomic number. (Full article...)
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